Iraqi Kurdish security forces have opened a road to Sinjar Mountain in northwestern Iraq, rescuing more than 5,000 Yazidis trapped there after running away from fighters from the Islamic State (IS) group, a Kurdish army spokesman has told Al Jazeera. 
 
 "I can confirm that we succeeded in reaching the mountains and opening a road for the refugees," said Halgord Hikmet, a spokesman for the Peshmergas, the Kurdish security forces. 
 
 Hikmet said that recent air strikes on IS targets by US warplanes had allowed the Peshmergas to open a route to the mountain. 
 
 The IS, which has captured large areas of Syria and Iraq, see Shia Muslims and minorities such as Christians and Yazidis, a Kurdish ethno-religious community, as infidels. 
 
 The Yazidis, a minority that follow a 4,000-year-old faith, had taken cover in Sinjar Mountain for the past five days in searing heat, and with no supplies, after fleeing advancing IS fighters. 
 
 Two Kurdish officials, Ekrem Hasso and Juan Mohammad, told the AP news agency that the Yazidis fled across the border from Iraq to seek refuge with the Kurds of northeastern Syria. 
 
 Rami Abdel-Rahman, who heads the London-based Syrian Observatory for Human Rights, also said thousands of people have fled from Iraq into Syria but had no exact number. 
 
 US warplanes have launched several waves of air strikes against IS fighters in northern Iraq since Friday. 
 
 Aerial drones and F-18 jets have attacked fighter positions close to the Kurdish capital of Erbil. 
 
 The air strikes seek to allow the federal and Kurdish governments to claw back areas lost in two months of conflict. 
 
 On Friday and Saturday, the US also dropped food and water for the Yazidis hiding on Sinjar Mountain. The UK is also delivering aid and has announced it is sending medics to northern Iraq. 
 
 'US troops will not fight in Iraq' 
 
 Barack Obama, the US president, said at a news conference on Saturday that Washington was proud to be acting alongside friends and allies in Iraq during the air strikes and was in the process of reaching Iraqi civilians trapped on Sinjar Mountain. 
 
 Obama repeatedly called on the Iraqis to come together to form a legitimate Iraqi government and overcome a political crisis that has been going on for months. 
 
 He also said that there was no particular timetable regarding the air strikes, adding that they would take place as long as it was necessary to protect Iraqi civilians and US citizens, diplomats and military advisers in Iraq. 
 
 Separately, in his weekly address earlier on Saturday, he said he would not allow the US to be dragged into another war in Iraq, making it clear that American combat troops will not return to fight there. 
 
 The air strikes are the first in the embattled country since Obama put an end to the US occupation in 2011 and come after the IS group made massive gains on the ground, seizing a major dam and forcing a mass exodus of religious minorities. ||||| Story highlights European militants who have traveled to Syria could go back home and launch attacks 
 
 So far, militants in Iraq and Syria haven't seen attacking the West as a priority 
 
 But officials also fear the conflict could create new terror ties, bomb technology, lone wolves 
 
 The U.S. air strikes carried out Friday against ISIS are likely to have one unintended consequence: immediately increase the terrorist threat in Europe and the United States, Western counter-terrorism officials tell CNN. 
 
 Within hours of U.S. military jets and drones conducting a strike on ISIS artillery that had been used against Kurdish forces defending Irbil, ISIS supporters called for retaliatory attacks against the United States. 
 
 "It is a clear message that the war is against Islam and the mujahideen. The mujahideen must strive and seek to execute proactive operations in their own home, America, to discipline America and its criminal soldiers," Abu al-Ayna al-Khorasani, an administrator of Shumukh al-Islam, the top-tier forum for ISIS propaganda, wrote on his account Friday, according to a translation by the SITE Intelligence group. 
 
 Other ISIS supporters railed against the United States using the Twitter handle #AmessagefromISIStoUS, posting images of the wreckage of the twin towers. "Don't forget 11 Sept .. Maybe US citizens want more like that," one extremist tweeted. In June after ISIS captured Mosul, its supporters had warned against strikes in a Twitter campaign #CalamityWillBefallUS. 
 
 Here are three ways ISIS and its supporters could retaliate for U.S. military action against its fighters: 
 
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 1. ISIS could unleash a crash program to attack the West 
 
 The nightmare scenario is that ISIS leaders initiate a crash program to launch attacks in the West. They are well-positioned to unleash such carnage if they choose. 
 
 ISIS, which calls itself the Islamic State but formerly was known as the Islamic State in Iraq and Syria, is thought to have tens of millions of dollars in cash reserves and it operates training camps on a scale last seen in Taliban-run Afghanistan. The 9/11 operation, by point of reference, cost $500,000. 
 
 European officials tell CNN up to 1,000 European extremists are believed to have joined ISIS. Dozens of Americans are probably fighting with the group, too. This gives ISIS the opportunity to train them and send them back home to launch attacks. 
 
 These European fighters also could pose a threat to the United States because many Europeans do not need a visa to enter the U.S. 
 
 There also are fears these Western fighters might be equipped with sophisticated devices that could evade airport security. Early this year, U.S. officials became worried that some AQAP bomb-makers trained by master-bombmaker Ibrahim al Asiri may have traveled to Syria. 
 
 This combination of threats was described by U.S. Attorney General Eric Holder as "more frightening than anything I think I've seen as attorney general," in an interview with ABC News several weeks ago. 
 
 So far, though, ISIS has not seen attacking the West as anything near a priority. 
 
 Its focus instead has been on expanding the territory it controls in Syria and Iraq. 
 
 The political turmoil brought about by the Arab Spring has made the ultimate dream of global jihadists -- the adoption of their kind of Islamic rule across the Arab world -- seem tantalizingly close. Attacking the West, which for al Qaeda leaders was always a means to this end, has become something of a sideshow. 
 
 It is possible that the limited aerial campaign initiated by U.S. President Barack Obama will not see a significant switch of focus from ISIS towards attacking the West. The White House's stated objectives do not include degrading the group. 
 
 ISIS -- previously known as al Qaeda in Iraq -- has never prioritized targeting Western soil, instead preferring to focus on fighting "infidels" at home. 
 
 In the decade since the Jordanian terrorist Abu Musab al-Zarqawi created the group, it has not been directly behind any plot on Western soil, even during the years the United States military engaged it in intense counter-insurgency operations across Iraq. 
 
 By contrast, in the decade after the September 11 terrorist attacks, al Qaeda operatives in Pakistani tribal areas provided wave after wave of Western recruits training on how to make bombs out of chemicals and components readily available in home-improvement and beauty-supply stores in the West. 
 
 To date, only one suspected ISIS recruit who has returned to Europe is alleged to have built such a device. 
 
 In February, French police arrested a man they identified as Ibrahim B., a 23-year-old French-Algerian, and retrieved three soda cans filled with nearly a kilogram (about two pounds) of the high explosive TATP from his Cannes apartment. French police suspect that in the 18 months he fought in Syria, he learned how to make TATP, an unstable and difficult-to-transport high explosive used to build detonators in multiple al Qaeda plots against the West. 
 
 It is not clear whether ISIS signed off on his alleged plot. 
 
 While some Western recruits are taught how to make improvised explosive devices in Syria, there is little indication yet that the group has created a training program tailored to attacking the West. The worry is that that could change. After a decade of insurgency in Iraq, no other group has more expertise in making IEDs. 
 
 2. Returned fighters could take matters into their own hands 
 
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 Photos: Photos: Syrian civil war in 2014 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A wounded child walks at a makeshift hospital in the rebel-held town of Douma after being injured in a reported airstrike by government forces on Tuesday, December 23. Douma, located near Damascus, has been under government siege for more than a year, with residents facing dwindling food and medical supplies.The United Nations estimates nearly 200,000 people have been killed in Syria since an uprising in March 2011 spiraled into civil war. Hide Caption 1 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A Christmas tree and a crèche made out of rubble are set up on a square in the, predominantly Christian, government-held Hamidiyeh neighborhood of Homs on Monday, December 22. Hide Caption 2 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrian children await medical treatment at a makeshift clinic in the besieged rebel town of Douma, on Sunday, December 21, near Damascus. Hide Caption 3 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A Syrian rebel fighter keeps an eye on government troops in Aleppo, Syria, on Wednesday, December 17. Hide Caption 4 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man drives his motorcycle through a puddle in Aleppo on Wednesday, November 26. Hide Caption 5 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A Syrian opposition fighter fires at Bashar al-Assad Regime forces in the Handarat district of Aleppo on Thursday, November 20. Hide Caption 6 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrian boys play in the ruins of a destroyed building in Aleppo on Tuesday, November 18. Hide Caption 7 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A wounded man is treated at a makeshift hospital in Damascus, Syria, following a reported air strike by government forces on Tuesday, November 11. Hide Caption 8 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Members of the Syrian Civil Defense carry an injured man after an alleged air strike in Aleppo on November 11. Hide Caption 9 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A member of the Syrian Civil Defense walks through a cloud of dust after an alleged air strike by government forces in Aleppo on November 11. Hide Caption 10 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A father cries over his son at a physical therapy center in Eastern al-Ghouta outside Damascus on Thursday, November 6. The boy had his leg tendons cut after he was injured in an airstrike four months before. Hide Caption 11 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A blindfolded man suspected of passing military information to the Syrian government waits to be interrogated by Free Syrian Army fighters Monday, October 6, in Aleppo. Hide Caption 12 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Medics at a field hospital in Douma, Syria, attend to a man who was injured in what activists said were two airstrikes carried out by forces loyal to Syrian President Bashar al-Assad on Saturday, September 20. Hide Caption 13 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Free Syrian Army fighters rest inside a damaged room in Aleppo on Tuesday, September 16, during what activists said were clashes with forces loyal to al-Assad. Hide Caption 14 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrian government forces walk down a street in Halfaya, Syria, after taking the city from rebel forces on Friday, September 12. Hide Caption 15 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Al-Qaeda-linked rebels from Syria gather around vehicles carrying U.N. peacekeepers from Fiji before releasing them Thursday, September 11, in the Golan Heights. The 45 peacekeepers were captured in the Golan Heights after rebels seized control of a border crossing between Syria and the Israeli-occupied territory. Hide Caption 16 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrian opposition fighters take position behind sandbags in Aleppo on Thursday, September 11. Hide Caption 17 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrians fleeing the violence stand next to their belongings as they attempt to cross into Turkey on Sunday, September 7. Hide Caption 18 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A boy looks at bodies lying outside a hospital after a barrel-bomb attack in Aleppo on Friday, September 5. Hide Caption 19 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A U.N. convoy moves in the buffer zone near the Golan Heights as they are escorted by Syrian rebel fighters near the Syrian village of Jubata Al Khashab on Tuesday, September 2. Hide Caption 20 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Residents of Aleppo remove a body from debris on Friday, August 29, after what activists claim was shelling by forces loyal to al-Assad. Hide Caption 21 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Druze men watch from the Golan Heights side of the Quneitra border with Syria as smoke rises during fighting between rebels and forces loyal to al-Assad on Wednesday, August 27. Hide Caption 22 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – This image was taken during a government guided tour in Mleiha, Syria, one day after Syrian government forces retook the town after a months-long battle with rebels, according to a military source and state television on Friday, August 15. Hide Caption 23 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Residents inspect the rubble of destroyed buildings in Aleppo after Syrian regime helicopters allegedly dropped barrel bombs there on Wednesday, August 13. Hide Caption 24 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Smoke trails over Aleppo following barrel bombs that were allegedly dropped by the Syrian regime on an opposition-controlled area on Monday, August 11. Hide Caption 25 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Photographs of victims of the Bashar al-Assad regime are displayed as a Syrian Army defector known as "Caesar," center, appears in disguise to speak before the House Foreign Affairs Committee in Washington. The briefing on Thursday, July 31, was called "Assad's Killing Machine Exposed: Implications for U.S. Policy." Caesar was apparently a witness to al-Assad's brutality and has smuggled more than 50,000 photographs depicting the torture and execution of more than 10,000 dissidents. Hide Caption 26 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrian rebel fighters take up positions behind sandbags in Aleppo on Wednesday, July 30. Hide Caption 27 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – People carry an injured man away from the site of an airstrike, reportedly carried out by Syrian government forces, in Aleppo on Sunday, July 27. Hide Caption 28 of 85 Photos: Photos: Syrian civil war in 2014 Hide Caption 29 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Rebel fighters execute two men Friday, July 25, in Binnish, Syria. The men reportedly were charged by an Islamic religious court with detonating several car bombs. Hide Caption 30 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A rebel fighter stands on a dust-covered street in Aleppo on Monday, July 21. Hide Caption 31 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man clears debris at the site of an alleged barrel-bomb attack in Aleppo on Tuesday, July 15. Hide Caption 32 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A woman walks amid debris after an airstrike by government forces July 15 in Aleppo. Hide Caption 33 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – People walk on a dust-filled street after a reported barrel-bomb attack in Aleppo on Monday, July 7. Hide Caption 34 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Apartments and other buildings lie in ruins on Tuesday, June 3, in Aleppo, a city that "has had the life bombed out of it," according to CNN's Nick Paton Walsh. Hide Caption 35 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man carries a girl injured in a reported barrel-bomb attack by government forces June 3 in Aleppo. Hide Caption 36 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A rebel fighter loads an anti-tank cannon outside Latakia, Syria, on Sunday, June 1. Hide Caption 37 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A rescue worker pulls a girl from rubble in Aleppo on June 1 after reported bombing by government forces. Hide Caption 38 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A giant poster of Syrian President Bashar al-Assad is seen in Damascus, Syria, on Saturday, May 31, as the capital prepares for presidential elections. Hide Caption 39 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Portraits of al-Assad dominate the cityscape in central Damascus on Tuesday, May 27. Al-Assad is firmly in power three years into the civil war, while the opposition remains weak and fragmented and extremists grow in numbers and influence. Hide Caption 40 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – The father of a 3-month-old girl weeps Monday, May 26, after she was pulled from rubble following a barrel-bomb strike in Aleppo. Hide Caption 41 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A woman stands in a heavily damaged building in Aleppo on May 26. Hide Caption 42 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – An injured man lies in a hospital bed after alleged airstrikes by government forces in Aleppo on Sunday, May 18. Hide Caption 43 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Buildings in Homs, Syria, lie in ruins Saturday, May 10, days after an evacuation truce went into effect. Thousands of displaced residents returned to the city. Hide Caption 44 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Rescuers carry a man wounded by a mine in the Bustan al-Diwan neighborhood of Homs on May 10. Hide Caption 45 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A Syrian woman carries a suitcase along a street in the Juret al-Shayah district of Homs on May 10. Hide Caption 46 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Residents carry their belongings in the al-Hamidieh neighborhood of Homs on May 10. Hide Caption 47 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A woman injured when a mine went off is carried in Homs on May 10. Hide Caption 48 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Residents return to damaged dwellings in Homs on May 10. Hide Caption 49 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Debris lies on a deserted street in Homs on Thursday, May 8. Hide Caption 50 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A mosque is seen through shattered glass in Homs, where an evacuation truce went into effect on Wednesday, May 7. Hide Caption 51 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A wounded man is treated at a makeshift hospital in Aleppo on Sunday, May 4. Hide Caption 52 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Debris rises in what Free Syrian Army fighters said was an operation to strike a checkpoint and remove government forces in Maarat al-Numan, Syria, on Monday, May 5. Hide Caption 53 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man helps a woman through debris after reported airstrikes by government forces on Thursday, May 1, in the Halak neighborhood of Aleppo. Hide Caption 54 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrians gather at the site of reported airstrikes in Aleppo on May 1. According to the Syrian Observatory for Human Rights, at least 33 civilians were killed in the attack. Hide Caption 55 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A woman runs after two barrel bombs were thrown, reportedly by forces loyal to Syrian President Bashar al-Assad in Aleppo on May 1. Hide Caption 56 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A boy runs in Aleppo on Sunday, April 27, after what activists said were explosive barrels thrown by forces loyal to al-Assad. Hide Caption 57 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Security and emergency medical personnel work at the site of a car bomb explosion Monday, April 14, in the Ekremah neighborhood of Homs. Hide Caption 58 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – In this photo released by the state-run SANA news agency, Syrian forces take positions during clashes with rebels near the town of Rankous, Syria, on Sunday, April 13. Hide Caption 59 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Flames engulf a vehicle following a car bomb Wednesday, April 9, in the Karm al-Loz neighborhood of Homs. Hide Caption 60 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man carries a child who was found in the rubble of an Aleppo building after it was reportedly bombed by government forces on Monday, March 18. Hide Caption 61 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – An elderly man and a child walk among debris in a residential block of Aleppo on March 18. Hide Caption 62 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A woman with blood on her face carries a child following a reported airstrike by government forces Saturday, March 15, in Aleppo. Hide Caption 63 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – People attempt to comfort a man in Aleppo after a reported airstrike by government forces on Sunday, March 9. Hide Caption 64 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Buildings in Homs lay in ruins on March 9. Hide Caption 65 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrian forces fire a cannon and a heavy machine gun loaded on a truck as they fight rebels in the Syrian town of Zara on Saturday, March 8. Hide Caption 66 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A handout photo released by SANA shows Syrian President Bashar al-Assad speaking March 8 during a meeting in Damascus to mark the 51st anniversary of the 1963 revolution, when Baath Party supporters in the Syrian army seized power. Al-Assad said the country will go on with reconciliation efforts along with its fight against terrorism. Hide Caption 67 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrians inspect the rubble of destroyed buildings in Aleppo following a reported airstrike by Syrian government forces on Friday, March 7. Hide Caption 68 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – People dig through the rubble of a building in Damascus that was allegedly hit by government airstrikes on Thursday, February 27. Hide Caption 69 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A boy walks ahead of men carrying the body of his mother in Aleppo on Saturday, February 22. According to activists, the woman was killed when explosive barrels were thrown by forces loyal to al-Assad. Hide Caption 70 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man holds a baby who survived what activists say was an airstrike by al-Assad loyalists Friday, February 14, in Aleppo. Hide Caption 71 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – In this photo provided by the anti-government activist group Aleppo Media Center, Syrian men help survivors out of a building in Aleppo after it was bombed, allegedly by a Syrian regime warplane on Saturday, February 8. Hide Caption 72 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrians gather at a site hit by barrel bombs, allegedly dropped by a regime helicopter on the opposition-controlled Mesekin Hananu district of Aleppo on February 8. Hide Caption 73 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – In this handout photo released by the state-run SANA news agency on February 8, civilians wave national flags in Damascus as they take part in a rally in support of President al-Assad. Hide Caption 74 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man stands next to debris in the road following a reported airstrike by Syrian government forces in Aleppo on February 8. Hide Caption 75 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Medical personnel look for survivors after a reported airstrike in Aleppo on Saturday, February 1. Hide Caption 76 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Syrians carry a dead body following an airstrike on February 1. Hide Caption 77 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man walks amid debris and dust on January 31. Hide Caption 78 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – An injured man is covered in dust after an airstrike on January 29. Hide Caption 79 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A man tries to fix electrical wires in Aleppo on January 27. Hide Caption 80 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Rebels and civilians check out a crater that activists say resulted from a Syrian government airstrike on an Aleppo bus station on Tuesday, January 21. Hide Caption 81 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Men rush to a site that Syrian government forces reportedly hit in Aleppo on January 21. Hide Caption 82 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – Buildings lie in ruins in Aleppo on Sunday, January 19, after reported air raids by Syrian government planes. Hide Caption 83 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A child collects items from a garbage pile in Douma, northeast of the capital, on Saturday, January 18. Hide Caption 84 of 85 Photos: Photos: Syrian civil war in 2014 Syrian civil war in 2014 – A piece of exploded mortar lies in a street in Daraya, a Syrian city southwest of Damascus, on Friday, January 17. Hide Caption 85 of 85 
 
 The most immediate threat to the West comes from hundreds of extremists who have returned home after fighting with terrorist groups in Syria. While little evidence has emerged so far that ISIS has directed them to launch attacks, their urban warfare skills would make them especially dangerous. 
 
 The first terrorist attack on Western soil linked to Syria probably followed this trajectory. Mehdi Nemmouche, a French-Algerian who spent a year in Syria and was recruited into ISIS, has been charged with gunning down four people at a Jewish museum in Brussels, Belgium, in May. ISIS itself did not claim responsibility for the attack, suggesting to investigators that Nemmouche planned the attack himself. 
 
 Among Western countries Europe has by far the greatest number of returnees. 
 
 "The threat of attacks has never been greater -- not at the time of 9/11, not after the war in Iraq -- never," a European counterterrorism official told CNN in June. He envisaged a flood of small-scale but effective and chilling attacks similar to the Brussels shooting. 
 
 European counterterrorism officials are worried the gains made by ISIS in Iraq will lead to a surge of travel to the region. In identifying who has traveled, they are often playing catchup. 
 
 "In most cases, we know within two weeks a guy has gone to Syria. But 10%-15% of the time, it can be several months before we figure it out. Inevitably, there will be some we have no idea about," one official told CNN. 
 
 But even those they know about are difficult to track. Nemmouche was on a watch list when he returned to Europe. European officials tell CNN it is impossible, because of the cost, to conduct 24-hour surveillance on any but a small fraction of people who have returned from Syria. 
 
 3. 'Lone wolves' could lash out 
 
 The Boston Marathon bombings illustrated the danger posed by extremists learning bomb-making skills over the Internet without having to travel to jihadist encampments overseas. 
 
 European officials say anger about events in Syria and Iraq and excitement about the gains made by ISIS have spiked radicalization to unprecedented levels across the continent. 
 
 Though the animus is not directed as squarely against the West as it was during the Iraq war, ISIS' viscerally anti-Western ideology is attracting a growing following in extremist circles in Europe. It matters little that European countries are not currently involved in air strikes: ISIS supporters believe all Western countries are working together to attack Islam. 
 
 The Costs of inaction 
 
 The likely increased terrorist threat in the West that will arise in the coming weeks and months from U.S. air strikes in Iraq should be weighed against the risks of letting ISIS grow unchecked. 
 
 If ISIS is able to consolidate its territorial gains, it could set up training camps to rival any run by al Qaeda in Afghanistan before 9/11. Though its focus may be in Iraq and Syria for now, its viscerally anti-Western ideology means it would be foolish to discount it as a major potential future threat. 
 
 Though the unfolding humanitarian crisis in Iraq may have left the Obama administration little choice but to act, the concern is the limited US aerial campaign has now stirred the hornet's nest without doing anything to decisively degrade ISIS. 
 
 And there could be one other unintended consequence. A rally-round-the-flag effect may now strengthen the ISIS position in the global jihadist movement, leading to even higher levels of fundraising and recruitment. 
 
 In recent months the group has faced fierce criticism from al Qaeda and others for its declaration of an Islamic caliphate and its brutal methods. But with the budding Islamic State now being bombarded by the "Crusaders," such criticisms may fade, at least for a time.
– In the wake of two US airstrikes against ISIS, supporters of the extremist group that's been seizing towns in northern Iraq are calling for retaliatory strikes against America, CNN reports. "It is a clear message that the war is against Islam and the mujahideen," wrote the administrator of an online ISIS forum. "The mujahideen must strive and seek to execute proactive operations ... to discipline America and its criminal soldiers." Other ISIS followers are deriding the US with the Twitter campaign #AmessagefromISIStoUS and posting photos of the 9/11 attacks (which isn't really new—they used the Twitter handle #CalamityWillBefallUS after ISIS took Mosul in June). Possible ways ISIS might strike the West include: A "crash" program: In this scenario, ISIS spends some of its tens of millions of dollars on arming European extremists who have joined the group (officials estimate there are up to 1,000 of them). This could reach American soil, because many Europeans can enter the US without a visa, and there's talk of sophisticated bombing devices that can slip past airport security. Returned fighters: Extremists who fought for ISIS in Syria and returned home "could take matters into their own hands," says CNN. Case in point: Mehdi Nemmouche, the French-Algerian accused of killing four people at a Jewish museum in Belgium this spring. "Lone wolves": The Boston Marathon bombing—enough said. Meanwhile, the effects of US military strikes aren't entirely clear, but the New York Times reports that almost two dozen ISIS fighters were killed and at least 30 injured near Mosul, and al Jazeera says the airstrikes have allowed Kurdish forces to reach Yazidi refugees on Sinjar Mountain and save more than than 5,000 of them. (See why President Obama says the Iraq intervention will be "long term.")