Ukraine's embattled president, Viktor Yanukovych, flew to Sochi late Thursday for crisis talks with Russian counterpart Vladimir Putin on the sidelines of the opening ceremony for the Winter Olympics.
Yanukovych left Kiev after holding talks with US Assistant Secretary of State Victoria Nuland as Moscow and Washington seek to influence a protracted crisis wracking the former Soviet nation.
"He has arrived," a source familiar with the situation told AFP ahead of Friday's opening ceremony for the Winter Olympic Games. "The talks (with Putin) can happen any time now."
The back-to-back meetings underlined the ratcheted-up struggle between Washington and Moscow to bring Ukraine into a Western or a Russian orbit, as Yanukovych seeks to weather more than two months of pro-Western demonstrations following his rejection of a key pact with the European Union.
Sharpening the tone, the Kremlin on Thursday accused the United States of arming Ukranian "rebels" and warned Russia could intervene to end the crisis.
"The stunts the Americans are pulling today by crudely interfering in Ukraine's domestic affairs in a unilateral manner are an obvious violation" of a 1994 treaty giving the US and Russia roles as security co-guarantors for Ukraine, Sergei Glazyev, Putin's economic adviser, told the Ukrainian edition of Russia's Kommersant.
When conflicts arise, the guarantors "are obliged to intervene," Glazyev said.
The hawkish adviser, who is viewed as the Kremlin pointman on Ukraine, added: "According to our information, American sources spend $20 million a week on financing the opposition and rebels, including on weapons."
He alleged that militants were briefed in the US embassy and being armed.
A Ukrainian activist who had been abducted in Ukraine last month told reporters the Lithuanian capital Vilnius that he had been "crucified" to a wooden door, and beaten until he was made to say he was an American spy.
"I told them that the American ambassador had given me 50,000 dollars," Dmytro Bulatov said in a hospital where he is undergoing treatment. "It was so scary, it was so painful that I asked them to kill me. I lied because I could not stand the pain."
The US embassy did not immediately comment on Glazyev's allegations, referring all questions to Nuland.
The US diplomat's visit came a day after EU foreign affairs chief Catherine Ashton said in Kiev Yanukovych's government was not doing enough to overcome Ukraine's worst crisis since independence in 1991.
After the meeting with Nuland, Yanukovych's office said the president supported swift constitutional reforms backed by protest leaders that would curb some of his powers.
But both the opposition and the West suspect the 63-year-old leader is playing for time.
Yanukovych in Olympic Sochi
In Russia's Black Sea city of Sochi, Yanukovych was expected to discuss a critical bailout deal for his crisis-hit country.
In December, Putin promised Yanukovych the $15 billion bailout but said last week the financing would not be released in full until the formation of a new government in Kiev.
The Ukrainian opposition slammed the meeting with Putin.
"Yanukovych is flying to the Olympics in Sochi at a time when it's necessary to solve the political crisis and defuse tension in society," boxer-turned-politician Vitali Klitschko said earlier Thursday.
The protests against Yanukovych broke out when the president in late November backed out of an EU trade and political association pact under Russian pressure.
Buoyed by Western support, the demonstrations spread and protesters dug in, earning concessions from Yanukovych -- notably the dismissal of the government and the scrapping of controversial anti-protest laws.
Since then, the protests have largely died down though activists remain barricaded in Kiev's central Independence Square.
On Thursday one opposition supporter in an occupied building had his hand blown off by a bomb blast, while another activist, 15, was hospitalised with eye burns.
With Yanukovych resisting calls to step down, the opposition is demanding the constitution be amended to curb presidential powers.
The crisis has seen the Ukrainian currency, the hryvnia, slump as residents scramble to convert their savings into other currencies.
The West is considering providing financing for Ukraine but one EU diplomat said it could not match Russia's aid.