EU leaders slammed Russia on Friday for meddling in its affairs after Ukraine rejected a landmark accord with the European Union designed to draw the ex-Soviet state into the Western fold.
The snub by Ukraine highlighted a worsening EU-Russia tug-of-war over former Soviet satellites in eastern Europe.
"The times of limited sovereignty are over in Europe," European Commission president Jose Manuel Barroso said at the close of the summit.
"We cannot accept... to have a kind of a possible veto of a third country. This is contrary to all principles of international law," he added.
The two-day summit in the Lithuanian capital on the EU's eastern flank was to have celebrated a five-year drive to cement ties between the bloc and Belarus, Ukraine, Moldova, Georgia, Armenia and Azerbaijan.
But Ukrainian President Viktor Yanukovych turned a deaf ear to pleas from the bloc's 28 leaders to go ahead with a far-reaching trade and political accord, saying economic pressure from Moscow, which is opposed to the deal, was hurting his nation's economy.
Thousands of pro-EU protestors turned out in Ukraine to denounce their leader's stand and call on him to resign.
Speaking to around 10,000 supporters, opposition leaders said Yanukovych had until mid-March to sign the political and free trade deal with the EU.
French President Francois Hollande pledged that the EU "door will always remain open for Ukrainians should they wish it."
Smaller Georgia and Moldova meanwhile initialled political and trade agreements that must still be officially signed in the coming months to come into effect.
New Georgian President Giorgi Margvelashvili called it "a historic day for Georgia, a historic day for Europe" but added "we are cautious" when asked whether he expected to come under Russian pressure too.
"We try to deliver the message to all capitals that prosperous, democratic Georgia can only be a benefit for any of Georgia's neighbours, including the Russian Federation," he said.
Global think-tank Stratfor warned however that "Russia has already begun to increase pressure on these states as well."
Kiev's surprise decision to scrap the landmark accord with the EU has unleashed a war of words between East and West recalling Cold War days and sparked some of the biggest protests seen in Ukraine in a decade.
Yanukovych's arch-foe, jailed former premier Yulia Tymoshenko, has said she would rather stay behind bars than see the country go East.
Tymoshenko's daughter Eugenia had told AFP that if Yanukovych "fails to sign the agreement... we cannot predict how people will react".
Keen to show Moscow's former communist satellites in Eastern Europe that the summit matters, almost all EU leaders attended the two-day talks, including the "Big Three" of Britain, France and Germany.
"It is our task in the future to talk even more with Russia about how we can overcome a situation where (a country) is either being tied closer to Russia or being tied closer to the EU," said German Chencellor Angela Merkel.
The EU's Eastern Partnership project aims to strike trade and aid deals on its eastern periphery and counter Russian influence, but vast Ukraine, with its 45 million people, industry and farms, was the major prize.
To make matters worse, Brussels has seen Armenia, Azerbaijan and Belarus turn back towards a Moscow which has reminded all of how much they stand to lose if they make what it sees as the wrong choice.
Brussels says that after months of arm-twisting by Moscow, Ukraine's exports to Russia dropped 25 percent, in some industries by 40 percent. Ukraine is also heavily dependent on Russia's natural gas.
[Image via Agence France-Presse]