Russia issued a new warning on Monday that it would retaliate if the European Union or Ukraine push ahead with moves to implement a free-trade agreement.
Kiev and Brussels agreed this month to delay implementation of the agreement until Dec. 31, 2015 after Russia threatened to impose import tariffs on Ukrainian goods if it went ahead.
Russia says its economy would be hurt by the free trade deal because it would allow Ukraine to export cheaper European goods to Russia, undercutting local products.
RIA news agency quoted Kremlin spokesman Dmitry Peskov as saying Russia was "ready to take measures in response if (implementation of the agreement) is carried out in violation of previously reached agreements."
He gave no details any possible measures.
Russia and the European Union are at loggerheads over Ukraine, where a Moscow-backed president was ousted in February following street protests, three months after he suspended the same pact and said he would boost ties with Russia instead.
Russia annexed the Ukrainian territory of Crimea after his replacement by a pro-European government in Kiev, and the West accuses Moscow of supporting pro-Russian separatists in Ukraine's east with weapons and troops. Moscow denies doing so.
The EU hopes that delaying the free-trade pact will give it time to assuage Russian concerns about it. Russia has said it wants three-way negotiations on amending the accord.