Thousands of people have staged fresh protests in Ukraine's capital, Kiev, at President Viktor Yanukovych's refusal to sign an EU association agreement.
Some 10,000 Demonstrators in Independence Square carried Ukrainian and EU flags late on Friday and chanted "Ukraine is Europe".
Mr Yanukovych, who attended an EU summit in Lithuania on Friday cited pressure from Russia for his decision.
A smaller rally in Kiev voiced support for the president's decision.
EU leaders meeting in the Lithuanian capital, Vilnius, warned on Friday they would not tolerate Russian interference in the bloc's relations with former Soviet republics.
"The times of limited sovereignty are over in Europe," said European Commission President Jose Manuel Barroso after a summit in Lithuania, at which provisional accords were reached with Georgia and Moldova.
'Stole our dream'
Last week, Mr Yanukovych announced he was suspending preparations for signing an association agreement in Vilnius, which would have opened borders to goods and set the stage for travel restrictions to be eased.
He argued Ukraine could not afford to sacrifice trade with Russia, which opposed the deal. He also described an EU offer to lend Ukraine 610m euros (£510m; $828m) as inadequate and said it would need at least 20bn euros a year to upgrade its economy to "European standards".
In comments reported on his website on Friday, Mr Yanukovych said he still intended to sign an agreement, but that there were "several crucial steps left to be made".
The daughter of jailed opposition leader Yulia Tymoshenko told the BBC on Friday that the president's reasons for not signing were "false".
She said her mother, who has begun a hunger strike against Mr Yanukovych's decision, had been refused access to her lawyer and they were increasingly concerned for her health.
Mr Yanukovych's decision to walk away from the EU deal brought thousands of protesters onto the streets of Kiev and the western city of Lviv on Friday evening.
Opposition leaders called for large-scale protests on Sunday in Independence Square - the epicentre of the 2004 Orange Revolution that forced a re-run of a disputed presidential election that had been won by Mr Yanukovych - and elsewhere.
"We will conduct massive protest actions in all of Ukraine. They must witness our strength," said Arseniy Yatsenyuk, an ally of Yulia Tymoshenko.
World boxing champion and prominent opposition figure Vitaly Klitschko told the crowd: "Today they stole our dream, our dream of living in a normal country."
Several small scuffles between protesters and the 2,000 riot police deployed around the square were reported, but no major clashes, according to the Associated Press.
There was also a smaller demonstration in support of Mr Yanukovych by about 3,000 to 4,000 people a few hundred metres away in Kiev's European Square.
"If we had signed, we would have opened our borders and killed our own manufacturers," Anatoliy Bliznyuk, an MP from Mr Yanukovych's Regions Party, told the Reuters news agency.
'Door always open'
EU leaders said in a statement that they "strongly" disapproved of Moscow's pressure on Ukraine not to sign - while Russian President Vladimir Putin accused the EU of "blackmail".
"I see this as a defeat for Ukraine," said Lithuania's President, Dalia Grybauskaite. "The current choice of the Ukrainian leadership means putting limits on the Ukrainian people's chances of achieving a better life."
EU Council President Herman Van Rompuy said the parties had been "really close" to signing the association agreement in Vilnius, but added: "We need to overcome pressure from abroad".
"We are embarked on a long journey, helping Ukraine to become, as others, what we call now, 'new member states'. But we have to set aside short-term political calculations."
German Chancellor Angela Merkel said the door would always remain open for Ukraine.