U.S. National security adviser Susan Rice has said Russian troops' intervention in Ukraine would be a 'grave mistake'.
Rice argued that a return to a Cold War posture would not reflect modern realities.
According to the Washington Post, during a wide-ranging interview on NBC's 'Meet the Press,' Rice said this was not about the US and Russia, but about whether the people of Ukraine.
She added that Ukrainians have the opportunity to fulfil their aspirations and be democratic and be part of Europe, which they choose to be.
On Saturday, the Ukraine parliament voted to oust President Viktor Yanukovych, who defiantly vowed to stay in power in a taped message.
According to the report, the exact whereabouts of the former leader have been unknown since Friday evening, but Rice said he has fled the Ukraine capital, Kiev, and appears unlikely to return soon.