LAKE SELIGER Russia/KIEV (Reuters) - Ukraine called on Friday for full membership in NATO, its strongest plea yet for Western military help, after accusing Russia of sending in armored columns that have driven back its forces on behalf of pro-Moscow rebels. 
 
 Russian President Vladimir Putin, defiant as ever, compared Kiev's drive to regain control of its rebellious eastern cities to the Nazi invasion of the Soviet Union in World War Two. He announced that rebels had succeeded in halting it, and proposed that they now permit surrounded Ukrainian troops to retreat. 
 
 Speaking to young people at a summer camp, Putin told his countrymen they must be "ready to repel any aggression towards Russia." He described Ukrainians and Russians as "practically one people," language that Ukrainians say dismisses the very existence of their thousand-year-old nation. 
 
 The past 72 hours have seen pro-Russian rebels suddenly open a new front and push Ukrainian troops out of a key town in strategic coastal territory along the Sea of Azov. Kiev and Western countries say the reversal was the result of the arrival of armored columns of Russian troops, sent by Putin to prop up a rebellion that would otherwise have been near collapse. 
 
 Rebels said they would accept Putin's proposal to allow Kiev forces, who they say are surrounded, to retreat, provided the government forces turn over weapons and armor. Kiev said that only proved that the fighters were doing Moscow's bidding. 
 
 Russia drew a fresh rebuke from French Foreign Minister Laurent Fabius, who told French television station France 24 that Russia could face more sanctions from the European Union. 
 
 "When one country sends military forces into another country without the agreement and against the will of another country, that is called an intervention and is clearly unacceptable," he said. 
 
 In Berlin, German Foreign Minister Frank-Walter Steinmeier said after speaking with his Ukrainian counterpart: "The border violations we are seeing – yesterday and even more so the day before yesterday – make us fear that the situation is increasingly getting out of control." 
 
 In Washington, White House spokesman Josh Earnest said Russia's footprint was undeniable in Ukraine. 
 
 "We have regularly marshalled evidence to indicate what exactly is happening, despite the protestations of the Russian government that for some reason would have us all believe otherwise," he said. "The fact is, those denials are completely without any credibility, and, you know, we've been pretty candid about that." 
 
 Full Ukrainian membership of NATO, complete with the protection of a mutual defense pact with the United States, is still an unlikely prospect. But by announcing it is now seeking to join the alliance, Kiev has put more pressure on the West to find ways to protect it. NATO holds a summit next week in Wales. 
 
 In 2008 NATO denied Ukraine and Georgia a fast track towards membership. Russia invaded Georgia a few months later. 
 
 NATO Secretary General Anders Fogh Rasmussen said he respected Ukraine's right to seek alliances. 
 
 "Despite Moscow's hollow denials, it is now clear that Russian troops and equipment have illegally crossed the border into eastern and southeastern Ukraine," Rasmussen said. "This is not an isolated action, but part of a dangerous pattern over many months to destabilize Ukraine as a sovereign nation." 
 
 In Donetsk, one of the main separatists strongholds, several shells exploded in the area of the railway station on Friday, one hitting the station building and another striking a trolleybus. 
 
 Rebel fighters quoted medics as saying emergency services had taken away four wounded people, and an unknown number had been ferried away in private cars. 
 
 Powerful explosions could be heard again in the center of town. A trolleybus was on fire on the square outside the station. Thick smoke filled the area. 
 
 The station has not been working for several days because damaged tracks are preventing trains from running. 
 
 Kiev said it was rallying to defend the port of Mariupol, the next big city in the path of the pro-Russian advance in the southeast. 
 
 "Fortifications are being built. Local people are coming out to help our troops, to stop the city being taken. We are ready to repel any offensive on Mariupol," military spokesman Andriy Lysenko said. 
 
 So far, the West had made clear it is not prepared to fight to protect Ukraine but is instead relying on economic sanctions, first imposed after Russia annexed Ukraine's Crimea peninsula in March and tightened several times since. 
 
 Those sanctions seem to have done little to deter Putin, leaving Western politicians to seek tougher measures without crippling their own economies, particularly in Europe which relies on Russian energy exports. 
 
 European foreign ministers met in Milan on Friday ahead of a weekend EU summit. They made clear the bloc will discuss further economic sanctions against Moscow. Some said that was no longer sufficient, and other measures to help Kiev should be discussed. 
 
 Polish Foreign Minister Radoslaw Sikorski said countries that had tried so far to mediate now needed to explain "what their ideas (are) to stop President Putin and save Ukraine as she is". Sweden's Carl Bildt said: "Sanctions alone are not enough: he (Putin) is prepared to sacrifice his own people." 
 
 Poland denied permission for Russia's defense minister to fly over its air space after a trip to Slovakia, forcing him to return to Bratislava. Warsaw said he could fly if he reported the status of his plane as civilian rather than military. 
 
 'BEST NOT TO MESS WITH US' 
 
 Moscow still publicly denies its forces are fighting to support pro-Russian rebels who have declared independence in two provinces of eastern Ukraine. But the rebels themselves have all but confirmed it, saying thousands of Russian troops have fought on their behalf while "on leave". 
 
 NATO has issued satellite photos of what it says is artillery fielded by more than 1,000 Russian troops fighting in Ukraine. Kiev has released interviews with captured Russian troops. 
 
 Reuters has seen an armored column of Russian troops on the Russian side of the frontier, showing signs of having recently returned from battle with no insignia on their uniforms. Members of an official Russian human rights body say as many as 100 Russian soldiers died in a single battle in Ukraine in August. 
 
 Encouraged by state media, Russians have so far strongly backed Putin's hard line, despite Western sanctions that have hurt the economy, the Kremlin's own ban on imports of most Western food, and now reports of Russian troops dying in battle. 
 
 In a statement released by the Kremlin overnight, Putin pointed to the rebels' gains of recent days on the battlefield: "It is clear that the rebellion has achieved some serious successes in stopping the armed operation by Kiev." 
 
 "I call on the militia forces to open a humanitarian corridor for encircled Ukraine servicemen in order to avoid pointless victims, to allow them to leave the fighting area without impediment, join their families," he said. 
 
 Putin's lengthy public appearance on Friday and his overnight statement on the conflict appear to be an acknowledgment that the war has reached a turning point, potentially requiring greater Russian sacrifice. 
 
 Putin answered questions from young supporters, some of whom waved banners bearing his face, at a pro-Kremlin youth camp on the shores of a lake. Wearing a grey sweater and light blue jeans, he looked relaxed but his tone grew intense while he spoke about Russia's military might, reminding the crowd that Russia was a strong nuclear power. 
 
 "Russia's partners ... should understand it's best not to mess with us," Putin said. 
 
 Putin compared Kiev's assault on the rebel-held cities of Donetsk and Luhansk to the 900-day Nazi siege of Leningrad in which 1 million civilians died, perhaps the most powerful historical analogy it is possible to invoke in Russia. 
 
 "Small villages and large cities surrounded by the Ukrainian army which is directly hitting residential areas with the aim of destroying the infrastructure," he said. "It sadly reminds me the events of the Second World War, when German fascist ... occupiers surrounded our cities." 
 
 He said the only solution to the conflict was for Kiev to negotiate directly with the rebels. Kiev has long refused to do so, arguing that the rebels are not a legitimate force on their own but proxies for Moscow, which must agree to rein them in. 
 
 RADICALLY DETERIORATING 
 
 Alexander Zakharchenko, leader of the main rebel group, told a Russian television station his forces were ready to let the encircled Ukrainian troops pull out, provided they leave behind their heavy armored vehicles and ammunition. 
 
 In Kiev, President Petro Poroshenko held an urgent meeting with security advisers overnight, after cancelling a trip to Turkey due to the "radically deteriorating situation".Prime Minister Arseny Yatseniuk told a government meeting on Friday the cabinet would "bring before parliament a law to scrap the non-aligned status of the Ukrainian state and establish a course towards membership of NATO". 
 
 Were NATO to extend its mutual defense pact to Ukraine, it would be the biggest change in the security architecture of Europe since the 1990s. After the Cold War, NATO defied Russian objections and granted its security guarantee to ex-Communist countries like Poland, Hungary and Romania. But it largely stopped at the border of the former Soviet Union, admitting only the three Baltic states Latvia, Lithuania and Estonia. 
 
 This year, after Putin annexed Crimea, NATO countries including the United States have repeatedly said they would be prepared to go to war to protect any member, but not to defend non-member Ukraine. 
 
 Kiev hopes to get its message across to Russians that their government is waging war without telling them. Ukrainian Defence Minister Valery Heletey said many Russian soldiers had been captured and killed: "Unfortunately, they have been buried simply under building rubble. We are trying to find their bodies to return them to their mothers for burial." 
 
 Russia's Defence Ministry again denied the presence of its soldiers in Ukraine: "We have noticed the launch of this informational 'canard' and are obliged to disappoint its overseas authors and their few apologists in Russia," a ministry official told Interfax news agency. 
 
 (Additional reporting by Lisa Jucca, Francesca Landini, Maria Tsvetkova,; Anton Zverev, Gabriela Baczynska, Polina Devitt, Vladimir Soldatkin, Thomas; Grove, Adrian Croft, Andreas Rinke, Steve Holland and Pavel Polityuk; Writing by; Peter Graff; Editing by Giles Elgood, Bill Trott, Sandra Maler and Andrew Hay) ||||| MOSCOW (AP) — Russia's President Vladimir Putin on Friday called on pro-Russian separatists to release Ukrainian soldiers who have been surrounded by the rebels in eastern Ukraine. 
 
 Russian President Vladimir Putin, right, meets with South African President Jacob Zuma in the Novo-Ogaryovo residence outside Moscow, Russia, Thursday, Aug. 28, 2014. (AP Photo/RIA-Novosti, Alexei Druzhinin,... (Associated Press) 
 
 Pro-Russian rebels hold their guns as they patrol the Lenin square in the town of Donetsk, eastern Ukraine, Thursday, Aug. 28, 2014. Ukraine's president Petro Poroshenko called an emergency meeting of... (Associated Press) 
 
 People observe damage done to a house after shelling in the town of Donetsk, eastern Ukraine, Thursday, Aug. 28, 2014. Ukraine's president Petro Poroshenko called an emergency meeting of the nation's... (Associated Press) 
 
 Putin's statement came several hours after Ukraine accused Russia of entering its territory with tanks, artillery and troops, and Western powers accused Moscow of lying about its role and dangerously escalating the conflict. 
 
 NATO said at least 1,000 Russian troops are in Ukraine and later released what it said were satellite photos of Russian self-propelled artillery units moving last week. 
 
 Russian Foreign Minister Sergey Lavrov dismissed the accusations of an invasion in a televised news conference on Friday, saying that Moscow "has not been presented with any facts" proving that it had happened. 
 
 For the second day, Russian markets reacted nervously to the escalation of the conflict in Ukraine with the Russian ruble diving to the all-time low of 37.10 rubles against the U.S. dollar in early morning trading, but recovered later to 36.90 rubles. 
 
 Markets dropped on Thursday on reports of Russia's apparent invasion in Ukraine, sparking investors' fears of further economic sanctions directed at Moscow. The ruble lost 1.4 percent against the dollar and the MICEX benchmark shed 1.6 percent. 
 
 "I'm calling on insurgents to open a humanitarian corridor for Ukrainian troops who were surrounded in order to avoid senseless deaths," Putin said in the statement published on the Kremlin's web-site in the early hours on Friday. 
 
 Putin did not address the claims about Russia's military presence in Ukraine. Instead, he lauded the pro-Russian separatists for "undermining Kiev's military operation which threatened lives of the residents of Donbass and has already led to a colossal death toll among civilians." 
 
 Putin's statement could be referring to Ukrainian troops who have been trapped outside the strategic town of Ilovaysk, east of Donetsk, for nearly a week now. Protesters rallied outside the Ukrainian General Staff on Thursday, demanding reinforcements and heavy weaponry for the troops outside Ilovaysk, most of whom are volunteers. 
 
 A top rebel leader in the rebel stronghold of Donetsk promptly reacted to Putin's appeal but said the Ukrainian troops would have to lay down the arms before they were allowed to go. 
 
 "With all our respect to Vladimir Vladimirovich Putin, the president of a country which gives us moral support, we are ready to open humanitarian corridors to the Ukrainian troops who were surrounded with the condition that they surrender heavy weaponry and ammunition so that this weaponry and ammunition will not be used against us in future," Alexander Zakharchenko said on Russia's state Rossiya 24 television. 
 
 The U.N. human rights office on Friday accused both sides of deliberately targeting civilians. 
 
 Pro-Russian rebels in Ukraine have carried out murders, torture and abductions along with other serious human rights abuses and violations of international humanitarian law, according to the mission's field work between July 16 and Aug. 17. The report also said Ukraine's military is guilty of human rights violations such as arbitrary detentions, disappearances and torture. 
 
 U.N. Assistant Secretary-General for Human Rights Ivan Simonovic, who visited Kiev on Friday, said the death toll had reached nearly 2,600 by Aug. 27, and described the humanitarian situation in eastern Ukraine as "alarming." 
 
 Simonovic condemned rebels for preventing people from leaving cities caught up in the fighting. He also pointed to reports of violations by volunteer battalions under government control. 
 
 In a talk Friday afternoon, Putin compared Ukrainian troops firing at civilians and surrounding cities in eastern Ukraine to Nazi invaders who laid siege to the Soviet siege of Leningrad in 1941-1944. He said residents of Ukraine's east were "suppressed with force" because they disagreed with what he called a coup in Kiev in February. 
 
 To stop the bloodshed, the Kiev government should open talks with the rebels who took up arms in defense, he said. 
 
 Two columns of tanks and other equipment entered southeastern Ukraine at midday on Thursday, following heavy shelling of the area from Russia that forced overmatched Ukrainian border guards to flee, according to Col. Andriy Lysenko, a spokesman for Ukraine's national security council. 
 
 European Union foreign ministers met in Milan Friday to weigh the 28-nation bloc's stance amid increasing calls to beef up economic sanctions against Russia. Their discussion was expected to prepare possible further steps to be announced at a summit of the bloc's leaders Saturday in Brussels. 
 
 U.S. President Barack Obama spoke Thursday with German Chancellor Angela Merkel, who has been a key power broker between the West and Russia, and they agreed Russia must face consequences for its actions. 
 
 Obama said Russia's activity in Ukraine would incur "more costs and consequences," though these seemed to be limited to economic pressure that will be discussed when Obama meets with European leaders at a NATO summit in Wales next week. 
 
 In a phone conversation with Ukraine's President Petro Poroshenko late Thursday, Merkel assured the Ukrainian leader of her support for "decisive actions" that could be taken Saturday, Poroshenko's press office said. 
 
 In Donetsk, the largest city under rebel control, the mayor's office reported sustained shelling across town on Friday morning. No casualties were immediately reported. 
 
 __ 
 
 Jim Heintz contributed to this report from Kiev, Ukraine. ||||| Media playback is unsupported on your device Media caption Nato Secretary General Anders Fogh Rasmussen: "Russia is blatantly violating Ukrainian sovereignty" 
 
 Nato has accused Russia of a "blatant violation" of Ukraine's sovereignty and engaging in direct military operations to support pro-Russian rebels. 
 
 Secretary-General Anders Fogh Rasmussen said that "despite hollow denials", it was now clear that Russia had illegally crossed Ukraine's border. 
 
 He said Nato would respect any Ukrainian decision on security, after its PM said he was putting the country on course for Nato membership. 
 
 Russia denies sending troops and arms. 
 
 Russian President Vladimir Putin blamed the Ukrainian government for the crisis, comparing its siege of two cities held by separatists, Donetsk and Luhansk, to the siege of Leningrad by Nazi Germany in World War Two. 
 
 "It is necessary to make the Ukrainian authorities start substantial talks [with the rebels]," he said. 
 
 Media playback is unsupported on your device Media caption Putin: "The situation sadly reminds me of the Second World War" 
 
 Nearly 2,600 people have been killed since April, the UN says, when Russia's annexation of Crimea prompted the rebels to take control of large parts of Donetsk and Luhansk regions. 
 
 Heavy fighting is continuing near Ukraine's strategic port of Mariupol, on the Azov Sea. Rebel forces are trying to capture the city but Ukrainian government troops are digging in. 
 
 The rebel advance there has raised fears that the Kremlin might seek to create a land corridor between Russia and Crimea. 
 
 On Thursday the separatists seized the nearby town of Novoazovsk. 
 
 Separatists are also reported to have surrounded government soldiers in several places further north, near Donetsk city. 
 
 Ukrainian forces near the town of Ilovaysk say they are cut off and have been urgently asking for supplies and reinforcements. 
 
 Image copyright AFP Image caption Ukraine has long insisted Russian is sending troops and hardware to support eastern rebels 
 
 Image copyright AFP Image caption Residents of Mariupol are digging trenches to help Ukrainian soldiers defend the strategic port city 
 
 Image copyright AP Image caption An anti-war rally was held in Mariupol on Thursday 
 
 Image copyright Reuters Image caption Many buildings have been destroyed in heavy fighting in Donetsk region 
 
 Earlier, Ukrainian Prime Minister Arseny Yatsenyuk said the government was reopening the question of Nato membership. 
 
 He said it was sending a bill to parliament calling for Ukraine's non-aligned status to be cancelled, in effect paving the way for Ukraine to join Nato. 
 
 'Dangerous pattern' 
 
 Speaking at a news conference after an emergency meeting of Nato ambassadors, Mr Rasmussen said that it was clear Russia was engaged in direct military operations in Ukraine. 
 
 "This is not an isolated action, but part of a dangerous pattern over many months to destabilise Ukraine as a sovereign nation," he said. 
 
 "This is a blatant violation of Ukraine's sovereignty and territorial integrity. It defies all diplomatic efforts for a peaceful solution." 
 
 On Thursday, Nato had released satellite images it said showed columns of Russian armed forces inside Ukrainian territory, adding that more than 1,000 Russian troops were operating inside Ukraine. 
 
 Image copyright Reuters Image caption This satellite image provided by the Supreme Headquarters Allied Powers Europe shows what Nato identifies as Russian self-propelled artillery in Ukraine 
 
 Mr Rasmussen called on Russia to cease military action, stop supporting the rebels and "take immediate and verifiable steps towards de-escalation of this grave crisis". 
 
 Mr Rasmussen indicated Nato was open to considering Ukraine's application to join if it met the conditions. 
 
 In 2008, Ukraine applied for Nato membership under then-President Viktor Yushchenko. 
 
 But the plans were shelved two years later when Viktor Yanukovych came to power and ended Ukraine's Nato ambitions in favour of mending relations with Russia. 
 
 Mr Rasmussen said on Friday: "I am not going to interfere with political discussions in Ukraine, but let me remind you of Nato's decision taken at the Bucharest Summit in 2008 according to which Ukraine will become a member of Nato, provided of course that Ukraine so wishes and provided that Ukraine fulfils the necessary criteria." 
 
 Analysis: Paul Adams, BBC News 
 
 Ukraine's prospects for Nato membership seem dim. 
 
 The 2008 pledge, made at the insistence of then-US President George W Bush, was criticised at the time. Some saw it as rash and needlessly provocative towards Moscow, which has long argued that the West broke a promise not to extend the alliance into the former Soviet bloc after the end of the Cold War. 
 
 Georgia's brief war with Russia, in the summer of 2008, convinced sceptics that for Nato to embrace countries with unresolved territorial disputes with Russia was not worth the risk. 
 
 And while the Ukrainian government wants it, what evidence is there that enough Ukrainians share the same enthusiasm? Opinion polls in 2008 suggested only about 30% of the population favoured membership. In the midst of Ukraine's worsening civil war, opinion is unlikely to be less divided. 
 
 Image copyright AFP Image caption A new UN report says civilians are being deliberated targeted in the fighting 
 
 A UN report released on Friday found that serious human rights abuses had been committed by rebels and Ukrainian forces. 
 
 The abuses include the deliberate targeting and killing of civilians trapped in urban areas or trying to flee the fighting via government-established "safe corridors", the study found. 
 
 It said that an average of around 36 people had been killed on a daily basis between 16 July and 17 August. 
 
 War in eastern Ukraine: The human cost 
 
 At least 2,593 people had been killed since mid-April, not including the 298 passengers and crew of the Malaysian Airlines MH17 shot down in the area, a UN report on 7 August said 
 
 951 civilians have been killed in Donetsk region alone, the official regional authorities said on 20 August 
 
 Official casualty counts only record certified deaths while in some particularly dangerous parts of the war zone, such as Luhansk region, victims are said to have been buried informally, for instance in gardens 
 
 Rebels (and some military sources) accuse the government of concealing the true numbers of soldiers killed 
 
 155,800 people have fled elsewhere in Ukraine while at least 188,000 have gone to Russia. 
 
 Have you been affected by what's going on in Ukraine? Tell us your story by emailing us at haveyoursay@bbc.co.uk
– Moscow continues to insist it's got nothing to do with the Russian soldiers and tanks that have entered Ukraine to bolster pro-Russian separatists, but Vladimir Putin today made a point to praise the separatists' military moves. They have "achieved serious successes in stopping the armed operation by Kiev," said the Russian president in a message on the Kremlin website, reports Reuters. He also urged the rebels to let trapped Ukrainian soldiers retreat safely, reports the AP: "I call on the militia groups to open a humanitarian corridor for Ukrainian service members who have been surrounded, so as to avoid any needless loss of life, giving them the opportunity to leave the combat area unimpeded and reunite with their families, to return them to their mothers, wives, and children, and to quickly provide medical assistance to those who were injured in the course of the military operation." The rebels appear ready to comply with what the New York Times calls a "rare direct address" from Putin. "With all respect to Vladimir Vladimirovich Putin, the president of the country, which has helped us very much with moral support, we are ready to grant humanitarian corridors to the Ukrainian divisions surrounded in these pockets," said one leader. NATO, meanwhile, accused Russia of a "blatant violation" of its neighbor's sovereignty, reports the BBC, much as President Obama did yesterday. Secretary-General Anders Fogh Rasmussen dismissed Moscow's "hollow denials" that it hadn't deliberately sent troops over the border. Further sanctions will be on the table at an EU summit this weekend.