Kiev's surprise decision days before the summit to scrap a landmark political and trade deal with the European Union that was years in the making, set off a war of words between East and West, and sparked the biggest protests seen in Ukraine in a decade.
Ukrainian President Viktor Yanukovych has pledged nonetheless to join leaders of the 28-nation bloc at the two-day Eastern Partnership summit in the capital of Lithuania, one of several ex-Soviet EU states campaigning to extend the bloc's sphere of influence.
Prime Minister Mykola Azarov's announcement failed to appease protesters who blockaded the government building during yesterday's cabinet session demanding Kiev sign the political and free trade deal at the two-day summit in Vilnius.
Keen to show eastern Europe that the summit matters, almost all EU leaders will attend despite the snub -- including the EU "Big Three", Britain, France and Germany.
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As the EU-Russia tussle flared, German Chancellor Angela Merkel told Russia not to view Europe's ties with Moscow's neighbours as a threat.
At stake are ties also with Armenia, Azerbaijan, Georgia, Moldova and Belarus -- keen to strike trade and aid deals or win visa-free travel arrangements with the EU.
But vast Ukraine, with its 45 million people, industry and farms, was the jewel in the crown of the EU's five-year-old Eastern Partnership policy. "If UKraine drops out it will be a glass half empty," said Steven Blockmans of the Centre for European Policy Studies.