Deep disagreement over the issue has led to the worst crisis between the US and Russia since the Cold War.The West accuses Russia of aiding pro-Russian activists who have seized public buildings across the east.US President Barack Obama has warned Russia against support for further action by armed pro-Russian groups."What I have said consistently is that each time Russia takes these kinds of steps that are designed to destabilize Ukraine and violate their sovereignty, that there are going to be consequences," he said.Meanwhile, Ukraine's military operation against separatists has hit obstacles.Called an "anti-terrorist" operation by the Kiev government, it started on Tuesday and is designed to dislodge pro-Russia gunmen from local authority buildings in a swathe of cities and towns in eastern Ukraine.Pro-Russian activists want referendums on greater autonomy for the south-east or the right to join the Russian Federation.But in several districts, Ukrainian troops met vehement opposition on Wednesday from pro-Russia supporters, who object to the new government in Kiev.Reports from Mariupol in the south of the Donetsk region say a Ukrainian military unit was attacked with petrol bombs.Soldiers are reported to have opened fire in response and several people were wounded, including some police.In the city of Kramatorsk, six military vehicles were commandeered on Wednesday by gunmen, who disarmed the Ukrainian soldiers and sent some of them home on buses.One Ukrainian officer said he had not "come to fight" and would never obey orders to shoot his "own people".In another incident, several hundred residents of Pchyolkino, south of Sloviansk, surrounded a column of 14 Ukrainian military vehicles.After the crowd was reinforced by pro-Russian gunmen, negotiations ensued and the troops were allowed to drive their vehicles away, but only after agreeing to surrender the magazines from their assault rifles.Ukraine's "anti-terrorist" operation is looking more and more a non-event - or worse, an outright fiasco, reports the BBC's David Stern in Donetsk.The Geneva meeting is the first time that foreign ministers from the US, the EU, Ukraine and Russia will sit down for talks since the crisis began.The US and the EU want an end to the occupations in eastern Ukraine and for the estimated 40,000-strong Russian forces massed near the Ukrainian border to pull back.A US official, speaking as Secretary of State John Kerry arrived in Geneva, stressed that Russia must "take this opportunity to de-escalate" or face a tightening of sanctions.Ukrainian Foreign Minister, Andriy Deshchytsya, called on Russia "not to support terrorist activities in eastern Ukraine."As if to further illustrate the gulf between the West and Russia over the crisis, Russia's foreign ministry accused Washington of "the persistent unwillingness or inability to see reality as it is in fact, and in a striving to impose on the rest of the world a distorted perception of what is happening in southeast Ukraine."Russia, which strongly opposed the ousting of Ukraine's pro-Moscow President Viktor Yanukovych in February, has proposed a new constitution which devolves more power to the regions.Expectations for the talks are low, says the BBC's Gavin Hewitt in Geneva.NatoRussia's stance over eastern Ukraine and its annexation of Crimea in March continue to cause concern in Nato member countries with large Russian-speaking minorities, such as Latvia and Estonia.So Nato announced on Wednesday that it was beefing up its eastern members' defences.In Brussels, Nato Secretary General Anders Fogh Rasmussen promised "more planes in the air, more ships on the water, more readiness on the land".He called on Russia to make clear it did not "support the violent actions of well-armed militias or pro-Russian separatists in eastern Ukraine".On Thursday, Russian President Vladimir Putin holds his annual televised phone-in, taking calls from people across the country. This year, he will also be taking questions from residents of Crimea.(BBC)ANN.Az