Ukrainian opposition leaders have demanded to know what President Viktor Yanukovych has offered Russia in return for a major economic lifeline.
Russian President Vladimir Putin has agreed to buy billions of dollars worth of Ukrainian government bonds and slash the price Ukraine pays for Russian gas.
The announcement comes as Russia tries to stop Ukraine moving towards the EU.
Opposition leader Vitali Klitschko told pro-EU protesters in Kiev Viktor Yanukovych was betraying Ukraine’s independence.
“He has given up Ukraine’s national interests, given up independence,” Vitali Klitschko, a former boxing champion, told the crowd on Tuesday.
“[President] Yanukovych used our country as collateral. According to our sources, he has agreed to a bailout from Russia and put Ukrainian plants, strategic industries, heavy industries, aviation and energy manufacturers up as collateral against it. We want to know what exactly he did put up as collateral, and his reasons for doing it.”
He called on President Viktor Yanukovych to hold a snap election.
“Yanukovych said at our round-table talks that he is not afraid of an early election. If that’s the case, let him prove it in an honest fight,” he said.
Although details of the agreement are unclear, Oleh Tyahnybok, leader of an opposition far-right group, said Viktor Yanukovych had “pawned whole sectors” of the country’s economy to Russia.
Ukraine urgently needs to cover an external funding gap of up to $17 billion (12.3 billion euros) next year to avoid defaulting on its debts.
After talks between Vladimir Putin and Viktor Yanukovych in the Kremlin, it was announced Russia would buy $15 billion-worth of Ukrainian government bonds.
The cost of Russian gas supplied to Ukraine has been slashed from more than $400 (291 euros) per 1,000 cubic metres to $268.5.
Vladimir Putin said the assistance was not “tied to any conditions”.
He also said they had not discussed Ukraine joining a Moscow-led customs union with Belarus and Kazakhstan.
The US has warned the Ukrainian government that the deal with Russia would not satisfy the protesters.
German Chancellor Angela Merkel said ties with Russia should not prevent Kiev from looking West.
“At the moment it seems to be an either-or proposition. We need to put an end to this,” Angela Merkel told ARD TV.
“A bidding competition won’t solve the problem.”
The current agreement signed between Russia’s Gazprom and Ukraine’s Naftogaz amends a controversial 2009 deal signed by former Ukrainian PM Yulia Tymoshenko, for which she was jailed two years ago.