Russia will come under heightened diplomatic pressure Thursday as the UN Security Council and European leaders hold emergency talks on Ukraine, after the seizure of Crimea created the worst East-West crisis since the Cold War.
The EU summit in Brussels starts at 1030 GMT, when leaders will meet with Ukraine's prime minister Arseniy Yatsenyuk who took over after the ouster of president Viktor Yanukovych last month following three months of deadly protests.
Ahead of the summit the EU froze assets held by 18 Ukrainians accused of embezzlement, including ousted Moscow-backed Yanukovych and his son Oleksandr.
As the EU confers on the crisis, 40 unarmed military personnel are expected in Crimea in a mission by the Organization for Security and Co-operation in Europe to try to defuse tensions in the flashpoint region.
Later the 15-member UN Security Council will hold closed-door talks from 1930 GMT in New York, the body's fourth consultations on the subject since Friday.
During an acrimonious round of emergency talks Monday, Russia told other council members that Yanukovych had asked Moscow to dispatch troops to re-establish law and order in his country.
As a permanent member of the council, Russia holds veto power and can block the body's draft resolutions.
Highlighting the strains on the ground, UN special envoy to Crimea Robert Serry was forced to cut short a visit when he was confronted by unidentified gunmen on Wednesday, but was expected to return to Kiev soon.
Serry, who had been sent to the tense Black Sea peninsula by UN chief Ban Ki-moon, was confronted by armed men after visiting the Ukrainian naval headquarters in Crimea's capital Simferopol, he told CNN television.
Prevented from returning to his vehicle, Serry said the men who refused to identify themselves said "they have received orders.... to bring me immediately to the airport" although they declined to say from whom.
"They said it was in my own safety. I refused and a standoff ensued," he added, saying at one point his driver was pulled from the car.
Serry sought refuge in a local cafe with his assistant to phone the mission and then after a tense two-hour standoff, he was driven to the airport and boarded the first flight out of the region -- to Istanbul.
Pro-Russian forces also entered and took over parts of a Ukrainian missile base on Wednesday in the latest such incident on the peninsula, while a Ukrainian court ordered the arrest of Crimea's newly installed pro-Russian prime minister Sergiy Aksyonov for separatism.
Violent protests have also broken out in cities in mainly Russian-speaking eastern Ukraine, where several regional government buildings have been taken over by pro-Russian militants who have clashed with police.
But US Secretary of State John Kerry said he was hopeful of a "de-escalation" in the stand-off on the eve of the EU summit after meeting Russian counterpart Sergei Lavrov, who pressed for early elections in Kiev.
Yanukovych fled to Russia following a bloodbath in Kiev in which scores of protesters and police officers were killed and, although he insists he is the legitimate president, Moscow has signalled his time is over.
Western leaders have at the same time increased diplomatic pressure on Russia, with some threatening to boycott the G8 summit in Russia in June and NATO saying it will review a series of accords with Moscow.
More stringent sanctions against Russian officials have been mooted but their prospect is seen as unlikely, at least for now.
"The logic is to get out of the crisis, not sanctions," said a source from the entourage of French President Francois Hollande who will discuss the situation with British Prime Minister David Cameron, German Chancellor Angela Merkel and the 25 other European Union chiefs.
As part of the international diplomatic flurry surrounding Ukraine, Kerry was due to meet Lavrov again in Rome on Thursday to discuss Ukraine on the sidelines of a conference on Libya.
Kerry failed in an attempt to get Lavrov and Ukraine's interim foreign minister, Andriy Deshchytsya, to sit down for a meeting in Paris on Wednesday.
Pentagon chief Chuck Hagel said Wednesday that the United States will bolster military cooperation with Poland and Baltic states to show "support" for its allies following Russia's intervention in Ukraine.
The moves to expand aviation training in Poland and step up the US role in NATO's air patrols over Baltic countries were clearly designed to reassure alliance partners in Central and Eastern Europe following alarm at Russia's actions on the Crimean Peninsula.
The European leaders will try to stress the importance of "constructive dialogue" and "peaceful resolution" of the crisis -- the terms used by EU foreign ministers who held a meeting in Brussels earlier in the week.
The priority for the EU is to strengthen the near-bankrupt former Soviet republic and its government.
The European Commission on Wednesday announced a massive aid plan of "at least 11 billion euros ($15 billion), although France said money should only be disbursed after elections in Kiev planned for May 25.
The US House of Representatives will vote Thursday on authorising an aid package for Ukraine.
Meanwhile a US-based anchor for the Russia Today television network resigned live on air in protest at the deployment of Russia-backed forces in Ukraine.
Liz Wahl said during a broadcast that she could no longer work for a Moscow-funded network which she accused of "whitewashing" the actions of Russian leader Vladimir Putin.