Russian Prime Minister Dmitry Medvedev on Monday questioned the legitimacy of Ukraine's new leadership and said that Western countries which accept it are mistaken, in his first reaction to the transfer of power in Kiev.

Medvedev said that Russia was unable to accept the new authorities in Kiev as a partner for talks and could not negotiate with rebels "carrying Kalashnikovs".

"Strictly speaking, there is no one for us to communicate with there today. The legitimacy of a whole number of organs of power that function there raises great doubts," he was quoted as saying by Russian news agencies.

"Some of our foreign, Western partners think otherwise... this is some kind of aberration of perception when people call legitimate what is essentially the result of an armed mutiny," Medvedev said.

"If you consider people who swagger around Kiev in black balaclavas carrying Kalashnikovs to be a government, then we will find it difficult to work with such a government," he added.

Foreign Minister Sergei Lavrov on Sunday told US Secretary of State John Kerry that the opposition had "de-facto seized power".

Medvedev said Monday that Russia was prepared to honour its obligations to Ukraine if and when legitimate authorities appeared.

But he did not make it clear whether Moscow would complete the handover of a $15 billion bailout secured by now-ousted President Viktor Yanukovych in December.

"Those agreements that are legally binding must be fulfilled," Medvedev said.

Asked about the loan to Ukraine, he said: "We can discuss any topics with our Ukrainian partners, but we need to understand with whom to discuss," the Interfax news agency reported.

Russia last week said it would not release a scheduled tranche of the loan extended by Putin to Yanukovych until the situation cleared up.

Russia in addition granted Ukraine a giant cut in its gas bills and Medvedev was also vague about the future of this agreement.

"The decisions in the gas sphere that were taken have concrete time limits," he said.

"What will happen when these limits run out - that is a question to discuss with the leadership of Ukrainian companies and the Ukrainian government -- if it ever appears there."

Medvedev had on Thursday urged Yanukovych, who has now fled to an unknown location, not to be a "doormat."

So far, President Vladimir Putin has remained silent on this weekend's dramatic events in Kiev that blew up during Russia's showpiece Winter Olympic Games in Sochi.