Ukrainian President Viktor Yanukovych has faced calls to resign over a $15bn (€11bn) bailout from Russia, which the opposition and protesters said had sold the country out to its former Soviet masters.

Tens of thousands of protesters gathered in Kiev after Mr Yanukovych secured financial assistance and a gas price discount at talks with Russian President Vladimir Putin.

Russia said it will buy Ukrainian bonds under a deal that keeps Ukraine firmly in Russia's orbit and out of the European Union's grasp.

Some Ukrainians have questions about what Mr Yanukovych might have agreed to in secret.

Many of the protesters are angry Mr Yanukovych has spurned an offer of closer cooperation with Europe. They look on Russia with suspicion after living for decades under Soviet communist rule.

"I think the people will eventually have it their way. We will sign up to Europe. That's why I'm here," said Snezhana, a factory worker who spent the night on Kiev's snowy main square.

Irina Litvinianko, a businesswoman, said: "It's hard to imagine it could end up in anything else but a change of power."

Opposition leaders have called for mass rallies over the holiday season on the central square occupied for weeks by protesters, who have pitched tents behind tall barricades.

"He has given up Ukraine's national interests, given up independence," Vitaly Klitschko, an opposition leader and heavyweight boxing champion, told the crowd yesterday.

Ukraine needs money to cover an external funding gap of $17bn next year - almost the level of the central bank's depleted currency reserves - and avoid defaulting on its debts.

Underlining the depth of the problem, Russian Finance Minister Anton Siluanov said Russia would buy $3 billion worth of Ukrainian Eurobonds as early as the end of this week, marking the first instalment in debt purchases to total $15 billion.

However, the United States warned Ukraine the deal would not satisfy the protesters. German Chancellor Angela Merkel said ties with Russia should not prevent Ukraine from looking West.

"At the moment it seems to be an either-or proposition. ...We need to put an end to this," Ms Merkel told ARD TV.

"A bidding competition won't solve the problem."

Russian Foreign Minister Sergei Lavrov told parliament that the West was continuing to put "overt pressure" on Ukraine.

Mr Putin wants to bring Ukraine's big, mineral-rich market into a Eurasian Union he plans to build with Kazakhstan, Belarus and other ex-Soviet republics to match the economic might of the US and China. Without Ukraine, it looks much weaker.

Mr Putin also seems determined to stop Ukraine, by far the most populous former Soviet republic after Russia, from building a new and close relationship with the EU.