Image copyright AP Image caption Sunni fighters, among them the jihadists of Isis, have taken large swathes of western and northern Iraq 
 
 Sunni militants have seized another town in Iraq's western Anbar province - the fourth in two days. 
 
 Fighters of the Islamic State in Iraq and the Levant (Isis) captured Rutba, 90 miles (150km) east of Jordan's border, officials said. 
 
 They earlier seized a border crossing to Syria and two towns in western Iraq as they advance towards Baghdad. 
 
 The insurgents intend to capture the whole of the predominantly Sunni Anbar province, a spokesman told the BBC. 
 
 Iraq's government said on Sunday it had killed 40 militants in an air strike on the militant-held northern town of Tikrit, although witnesses said civilians died when a petrol station was hit. 
 
 US Secretary of State John Kerry, speaking in Cairo, said Isis' "ideology of violence and repression is a threat not only to Iraq but to the entire region". 
 
 Calling it a "critical moment", he urged Iraq's leaders "to rise above sectarian motivations and form a government that is united in its determination to meet the needs and speak to the demands of all of their people". 
 
 Earlier, Iran's supreme leader Ayatollah Ali Khamenei condemned the prospect of US intervention in Iraq, saying Washington's main intention was to keep Iraq within its own sphere of power. 
 
 Dismissing talk of sectarianism, he said: "The main dispute in Iraq is between those who want Iraq to join the US camp and those who seek an independent Iraq." 
 
 Analysis from BBC Persian's Bozorgmehr Sharafedin 
 
 The Obama administration is signalling that it wants a new government in Iraq without Prime Minister Nouri Maliki before launching any attack on Isis, but Iran's Supreme Leader has rejected both ideas. 
 
 Ayatollah Khamenei strongly opposed "the intervention of the US and others in the domestic affairs of Iraq", and said the US is not pleased with the results of the new election and "is seeking an Iraq under its hegemony and ruled by its stooges". 
 
 Khamenei's anti-US remarks weaken the possibility of co-operation. Iran feels it has the upper hand in Iraq and would try to resolve the crisis by the help of "Iraqi people, government and Shia clerics". 
 
 Rutba is strategically placed on the main road between Baghdad and Jordan. 
 
 It is the fourth town in what is Iraq's largest province to fall in two days to the Sunni rebel alliance, which Isis spearheads. 
 
 On Saturday the militants said they had taken the towns of Rawa and Anah, along the Euphrates river. 
 
 And Iraqi officials admitted Isis fighters had also seized a border crossing near the town of Qaim, killing 30 troops after a day-long battle. 
 
 According to the rebels, army garrisons, including at the area's command centre, abandoned their bases and weapons, and fled. 
 
 An Iraqi military spokesman described the withdrawal from Rawa, Anah and Qaim as a "tactical move... for the purpose of redeployment". 
 
 Isis in Iraq 
 
 Media playback is unsupported on your device Media caption Isis fighters have been pushing towards Iraq's capital, Baghdad 
 
 Isis grew out of an al-Qaeda-linked organisation in Iraq 
 
 Estimated 10,000 fighters in Iraq and Syria 
 
 Joined in its offensives by other Sunni militant groups, including Saddam-era officers and soldiers, and disaffected Sunni tribal fighters 
 
 Exploits standoff between Iraqi government and the minority Sunni Arab community, which complains that Shia Prime Minister Nouri Maliki is monopolising power 
 
 Isis led by Abu Bakr al-Baghdadi, an obscure figure regarded as a battlefield commander and tactician 
 
 Jihadi groups around the world 
 
 The capture of the frontier crossing could help Isis transport weapons and other equipment to different battlefields, analysts say. 
 
 The rebels are confident that towns they do not already control along the Euphrates valley will fall without much of a fight, with the help of sympathetic local tribes, says the BBC's Jim Muir in Irbil. 
 
 Since January, they have held parts of the provincial capital Ramadi, and all of nearby Falluja, half an hour's drive from Baghdad. 
 
 A spokesman for the Military Councils, one of the main Sunni groups fighting alongside Isis, told the BBC the rebels' strategic goal was the capital itself. 
 
 In the meantime they are clearly trying to take the string of towns along the Euphrates between Falluja and the western border, says our correspondent. 
 
 Baghdad fears 
 
 There is deep pessimism in Baghdad about the government's war against Isis, which appears better trained, equipped and more experienced than the army, diplomats and politicians have told the BBC. 
 
 The Sunni extremists attacked the city of Mosul in early June and have since seized swathes of territory across Iraq. 
 
 The Iraqi government has urged the US, Europe and the UN to take immediate action to help deal with the crisis - including targeted air strikes. 
 
 But Isis has established secure safe havens, including some in neighbouring Syria, which will be difficult to target, experts say. 
 
 And experts warn that using air strikes now would endanger civilians. 
 
 Media playback is unsupported on your device Media caption Shia cleric Moqtada al-Sadr has rallied followers to join a military parade across Iraq, as Jonathan Beale reports from Baghdad 
 
 The US, which pulled out of Iraq in 2011, is sending some 300 military advisers to Iraq to help in the fight against the insurgents there. 
 
 But the White House insists there is no purely military solution to the crisis. 
 
 Mr Obama believes Mr Maliki has endangered the country by ignoring Sunni concerns and governing in the interests of the Shia majority, correspondents say. 
 
 Are you in Iraq or do you have family there? Have you been affected by recent events? You can send details of your experiences to haveyoursay@bbc.co.uk using 'Iraq' in the subject line. ||||| BAGHDAD — The long lines of Shiite fighters began marching through the capital early Saturday morning. Some wore masks. One group had yellow and green suicide explosives, which they said were live, strapped to their chests. 
 
 As their numbers grew, they swelled into a seemingly unending procession of volunteers with rifles, machine guns and rocket-propelled grenades, backed by mortar crews and gun and rocket trucks. 
 
 The Mahdi Army, the paramilitary force that once led a Shiite rebellion against American troops here, was making its largest show of force since it suspended fighting in 2008. This time, its fighters were raising arms against the Islamic State in Iraq and Syria, or ISIS, the Qaeda splinter group that has driven Iraq’s security forces from parts of the country’s north and west. 
 
 Chanting “One, two, three, Mahdi!” they implored their leader, the cleric Moktada al-Sadr, to send them to battle. 
 
 “ISIS is not as strong as a finger against us,“ said one fighter, Said Mustafa, who commanded a truck carrying four workshop-grade rockets — each, he said, packed with C4 explosive. “If Moktada gives us the order, we will finish ISIS in two days.” 
 
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 Large sections of Baghdad and southern Iraq’s Shiite heartland have been swept up in a mass popular mobilization, energized by the fatwa of Grand Ayatollah Ali al-Sistani urging able-bodied Iraqis to take up arms against Sunni extremists. Shiite and mixed neighborhoods now brim with militias, who march under arms, staff checkpoints and hold rallies to sign up more young men. Fighting raged in northern and western Iraq on Saturday, with the Sunni insurgents making some gains near a strategic border crossing with Syria. 
 
 The Mahdi Army rally in the Sadr City neighborhood of Baghdad on Saturday was the largest and most impressive paramilitary display so far, but there were also mass militia parades in other cities, including Najaf and Basra on Saturday, and smaller rallies in Baghdad on Friday, equally motivated by what participants described as patriotic and religious fervor. 
 
 Together, the militias constitute a patchwork of seasoned irregulars who once resisted American occupation, Iranian proxies supported by Tehran, and pop-up Shiite tribal fighting groups that are rushing young men to brief training courses before sending them to fight beside the Iraqi Army against ISIS. 
 
 It is a mobilization fraught with passion, confusion and grave risk. 
 
 Militia members and their leaders insist they have taken up arms to defend their government, protect holy places and keep their country from breaking up along sectarian or ethnic lines. They have pledged to work alongside the Iraqi Army. 
 
 But as Iraq lurches toward sectarian war, the prominent role of Shiite-dominated militias could also exacerbate sectarian tensions, hardening the sentiments that have allowed the Sunni militants to succeed. 
 
 Moreover, some of the militias have dark histories that will make it hard for them to garner national support. Some commanders have been linked to death squads that carried out campaigns of kidnappings and killing against Sunnis, including from hospitals. 
 
 Against this background, even as more armed men have appeared on the streets, Shiite clerics have taken pains to cast the mobilization as a unity movement, even if it has a mostly Shiite face. 
 
 “Our mission is to explain to the people what Ayatollah Sistani said,” said Sheikh Emad al-Gharagoli, after leading prayers Thursday afternoon at the Maitham al-Tamar Mosque in Sadr City. “He said, ‘Do not make your own army, this army does not belong to the Shia. It belongs to all of Iraq. It is for the Shia, the Sunni, the Kurds and the Christians.’ ” 
 
 The clerics have also said the mobilization will be temporary, that the militias will be disbanded once the ISIS threat subsides. 
 
 Continue reading the main story Video 
 
 But given the swift gains by ISIS and the lax performance of the Iraqi Army, analysts do not expect the infusion of Shiite militias to quickly turn the tide. And as the militias focus on establishing themselves, their leaders face a host of daunting practical matters intended to convert a religious call to a coherent fighting force. 
 
 Sheikh Haidar al-Maliki, who is organizing fighters of the Bani Malik tribe in Baghdad, said he had been in constant consultation with the government to ensure that the tribe’s call-up ran efficiently. 
 
 He has been seeking letters from the army that volunteers can show their employers to protect their jobs while they are fighting, and asking for uniforms and weapons for the few men who have not appeared with their own. He said he was also asking for government-issued identification cards, so that as thousands of armed men head to and from battle, it might be possible to know who is who at checkpoints along the way. 
 
 The Bani Malik militia is new. The tribe’s volunteers, at one registration rally, showed up with mismatched weapons and uniforms. Many of the weapons were dated. Some were in disrepair. 
 
 Nonetheless, Sheikh Maliki said, in a week, he had already sent hundreds of young men to military bases, where they are trained for a few days before shipping out to provinces where the army has been fighting ISIS. 
 
 “We do it step by step,” he said. “But we work very quickly.” 
 
 His militias had already fought in Mosul and near Baquba, he said. On Thursday, the first of its members died of battle wounds. 
 
 Other young men have been lining up to replace the fallen. 
 
 Ahmed al-Maliki, 23, a business-management student, said he had begun military training more than a month ago, in anticipation that ISIS’s campaign would grow. 
 
 His training, even before Ayatollah Sistani’s June 13 call to arms, pointed to what Sheikh Maliki said was the Shiite tribes’ realization early this year, after ISIS seized Falluja, that they needed to prepare for clashes with Sunni extremists. 
 
 The recent call-up, he said, was a public step that invigorated a body of quieter work already well underway. 
 
 The Bani Malik tribe had organized volunteers into 25-man units, each led by an active-duty Iraqi soldier who had been training them in weapons, small-unit tactics and communications. 
 
 Ahmed al-Maliki said he had never served in the army, and did not fight as a militant during the American occupation from 2003 to 2011. 
 
 But in the preparatory system that his tribe had organized this spring, he had learned to use a Kalashnikov that his family owned and other weapons under the instruction of Mustafa al-Maliki, a three-year Iraqi Army veteran. 
 
 “I don’t have any experience in the army,” Ahmed said. “But I can serve my country and do as Ayatollah Sistani says.” 
 
 For the Mahdi Army, the mobilization has not been a matter of creating a militia, but of preparing fighters for battle again. 
 
 Many of its members marching on Friday and Saturday had combat experience. They appeared in uniforms and with many newer weapons, typically in a better state of cleanliness and repair. 
 
 One member, who gave only a first name, Ahmed, said he had been with the Mahdi Army since 2004, and fought many times. 
 
 A Mahdi Army leader, Hakim al-Zamili, a member of Iraq’s Parliament who was accused of organizing death squads when he served as Iraq’s deputy health minister, appeared with a Mahdi unit on Friday evening and said that he intended to fight ISIS personally. 
 
 Mr. Zamili had been captured and held by American forces, and was released only after an Iraqi government trial on terrorism charges stalled after witnesses did not appear. He suggested that experienced militias would prove more nimble than Iraq’s conventional army. 
 
 Photo 
 
 “Why do the terrorists win battles against the Iraqi Army?” he asked. “Because the army is afraid to do what it must. They don’t have the right leadership.” 
 
 “The Army waits for orders,” he continued. “But the militias will do it quickly. We can seize a place and then give it to the army.” 
 
 A Mahdi fighter, who declined to give his name, framed it another way. “There is a difference between army fighting and street fighting,” he said. “We are street fighters.” 
 
 On one point the militias have been firm: In interviews throughout the past week, clerics and fighters for different groups said they did not want American ground forces in Iraq again, even to fight ISIS. 
 
 Some of the militias said they would, however, welcome other forms of military aid, and did not oppose President Obama’s commitment to send military advisers to Baghdad. 
 
 “We need matériel, and guns, and intelligence, or drones,” Sheikh Maliki said. 
 
 The sheikh said Iraq would also need Washington’s political and diplomatic help, in particular to try to sever ISIS’s foreign support, including, he said, from donors in Persian Gulf states and Turkey. 
 
 “If America helps us in these ways,” he said, “we can stop them.” 
 
 Deep divisions remain between many Shiite tribes and militias, which have competed for resources, power and standing, and had varied relations with Iran and attitudes toward the West. At the Mahdi rollout on Saturday, fighters burned Israeli and American flags, along with the black banner of ISIS. 
 
 For now, Sheikh Maliki and Mr. Zamili said, the militias have set aside most of their disagreements to face a common foe. 
 
 “We have differences,” Mr. Zamili said. “But in front of our enemies, we are one.” ||||| A member of the board of governors of the Central Bank of Iraq was reluctant to specify how much ISIS got away with in Mosul, but estimated that it at least $85 million and possibly much more. He spoke on the condition of anonymity because he was not authorized to speak publicly about the case. 
 
 “ISIS gets some money from outside donors, but that pales in comparison to their self-funding,” said an American counterterrorism official. “The overwhelming majority of its money comes from criminal activities like extortion, kidnapping, robberies and smuggling. In Mosul, ISIS has probably been hauling in several million dollars monthly just from its extortion racket. In overrunning the town the group is better off financially, but probably to the tune of millions — not hundreds of millions — of dollars.” 
 
 While ISIS “is among the wealthiest terrorist groups on the planet,” the official said, “it also has significant expenses. Resources flowing into the group’s coffers tend to move out the door in the form of payments fairly quickly. Unless it has invested very wisely, it’s probably sitting on a pile of assets worth somewhere in the tens of millions of dollars.” 
 
 The militant group has so much cash that it has reopened some of the banks it looted in Falluja, in Anbar Province, to stash it in. Jassim Ahmed, 35, who works as a taxi driver in the city, which has been under militant control since January, said he asked one of the gunmen guarding the banks where the militants get their money. “Don’t ask me again,” the gunman told him, he said. “Just understand, we have a budget to administer all of Iraq, not just Anbar.” 
 
 Kamel Wazne, an analyst based in Beirut, Lebanon, who has followed the group’s development into a self-financing, territory-controlling entity, said: “We no longer have to imagine a terror state. We have one.” 
 
 ISIS started amassing a bankroll in Syria last year after it took over the eastern Syrian oil fields, near Raqqa. It operates primitive refineries to make products for local use by ISIS’s own fighters, but sells much of the crude to its enemy — the Syrian government. In Minbij, it runs a local cement factory, and in Raqqa merchants even pay the militants a trash collection fee.
– Officials in Baghdad are increasingly worried that the Iraqi Army is simply incapable of standing up to the Islamic State of Iraq and Syria, which is both better armed and better trained, diplomats and politicians tell the BBC. And the militants provided plenty of evidence for that as their campaign rolled on today, capturing their fourth town in two days. Rutba in Anbar Province lies on a key road between Baghdad and Jordan. Yesterday, they took two other towns along the Euphrates river. In other developments: Yesterday also saw the rebels seize a border crossing into Syria, the Wall Street Journal reports, giving them a potentially strategically crucial pipeline between their two staging grounds. But the corresponding checkpoint on the other side of the border is under the control of the al-Qaeda-affiliated al-Nusra Front, which is fighting ISIS for control of it—unlike the Iraqi Army, which simply fled its checkpoint. Iraq's government fired off an airstrike in Tikrit that it said killed 40 militants. But witnesses say many civilians were killed as the strike hit a gas station. Shiite volunteers are coming out of the woodwork in Baghdad, thanks to Grand Ayatollah Ali al-Sistani's call to arms, the New York Times reports. Muqtada al-Sadr's Mahdi Army put on a particularly strong paramilitary display in Sadr City yesterday. "ISIS is not as strong as a finger against us," one Mahdi fighter said. "If Muqtada gives us the order, we will finish ISIS in two days." But ISIS is gaining wealth and weapons with every target it takes. Even before it took over Mosul outright its extortion rackets there were generating $8 million a month, and now those rackets have transformed into "taxes." "We don't know the exact amount of money they stole from Mosul," one member of Iraq's parliament says. "But it is big, big enough that ISIS can use it to occupy other countries too." The militants are also pulling in donations from places like Saudi Arabia, thanks in part to their social media savvy. When they captured five American-made helicopters recently, for example, they cheekily tweeted, "We’ll expect the Americans to honor the warranty and service them for us."