The EU's top two officials have sharply criticised Russia for putting pressure on Ukraine to drop plans to sign a trade and co-operation agreement with the EU this week.
The statement came amid new clashes in Ukraine's capital Kiev between pro-EU demonstrators and police.
"It is up to Ukraine to freely decide what kind of engagement they seek with the European Union," the EU said.
"We therefore strongly disapprove of the Russian position and actions."
The statement was issued jointly by European Council President Herman Van Rompuy and European Commission President Jose Manuel Barroso.
They insisted that stronger ties with the EU would not undermine Ukraine's existing relations with other neighbours, such as Russia.
"The Eastern Partnership is conceived as a win-win where we all stand to gain," they said.
Russia has threatened unspecified economic measures if Ukraine signs the deal with the EU. In the past Moscow has suspended gas supplies, in disputes over prices, and this year it blocked imports of Ukrainian chocolates.
Russia has also boycotted wine and mineral water from Georgia and Moldova - two other ex-Soviet states seeking favourable trade terms with the EU.
Georgia and Moldova are expected to initial agreements with the EU at an Eastern Partnership summit in Vilnius, Lithuania, on 28-29 November.
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