Russia has threatened Ukraine with bankruptcy as it warned against signing a landmark trade and cooperation agreement with the European Union.
Speaking at a conference in the Black Sea city of Yalta, Russian presidential adviser Sergei Glazyev dismissed the benefits of a planned treaty as "mythology".
He warned that tariffs and trade checks thatRussiawould impose after the deal could cost Ukraine billions of dollars and result in a default.
"Who will pay for Ukraine's default, which will become inevitable?" Mr Glazyev asked. "One has to be ready to pay for that."
Saying that a default would cost Ukraine "25 or even 35 billion euros", he asked: "Would Europe take responsibility for that?"
Russia is opposing Kiev's plans to sign a free-trade and political association agreement with the 28-member bloc in November, which would be a major step towards possible eventual membership.
Determined not to lose sway over his neighbours, Vladimir Putin instead wants lure Kiev into the Moscow-led Customs Union for former Soviet states.
Moscow raised the pressure on Ukraine over the summer by banning the products of a major chocolate maker in Russia and by temporarily halting some Ukrainian imports at its border.
Petro Poroshenko, a former trade minister and confectionery magnate, clashed with Mr Glazyev at the 10th annual meeting in Yalta, organised by the pro-European Ukrainian billionaire Viktor Pinchuk over the weekend.
Mr Poroshenko lashed out at Russia for banning his products, adding that Moscow had previously resorted to similar tactics when dealing with other dissenting former Soviet republics.
"I am 100 per cent sure that nobody either in this forum, nor in the world, would strongly believe that Georgian mineral water or Moldovan wine or Ukrainian chocolate or Lithuanian cheese or Belarusian milk products are really harmful for the health of the Russian consumer. This is simply not true," he said.
EU officials have urged Kiev to implement key reforms and sign the EU deal in November, saying Ukraine belongs with the West.
The key obstacle to the deal is the incarceration of former Ukrainian Prime Minister Yulia Tymoshenko, whose verdict the West has condemned as politically motivated and is pressing hard for her to be released in order for the deal to be signed.
Radoslaw Sikorski, the Polish foreign minister, Ukraine to resist the Kremlin pressure, citing Poland's success in joining the EU.