U.S. Assistant Secretary of State Victoria Nuland arrived in Ukraine Thursday for talks with President Viktor Yanukovych and with supporters of the political opposition.
Nuland's visit comes a day after European Union foreign affairs chief Catherine Ashton visited the Ukrainian capital, Kyiv, as anti-government demonstrations continue.
President Yanukovych's decision to back off of an EU trade deal in favor of closer ties with Russia touched off weeks of political rallies. The demonstrations grew violent last month as protesters clashed with police. Several people have died in the clashes.
Russia has offered Ukraine a $15 billion financial aid package to help Ukraine survive its economic troubles, but has yet to come through with the money. Russian President Vladimir Putin said the funding would not be released in full until a new government is formed in Kyiv.
Meanwhile, Mr. Putin's adviser on regional integration has accused the United States of financing and arming Ukraine's "opposition and rebels."
In an interview with the newspaper Kommersant-Ukraine published Thursday, Sergei Glazyev alleged that U.S. "sources" are spending $20 million a week to provide such financing, including for weapons, and that Ukrainian anti-government militants are being trained "on the territory of the American embassy" in Kyiv.
He accused the United States of "unilaterally and crudely interfering in Ukraine's internal affairs."
Glazyev also claimed Russia has legal grounds to intervene in Ukraine, citing the 1994 Budapest Memorandum on Security Assurances, which named the United States and Russia as the guarantors of Ukraine's sovereignty and territorial integrity.
He did not specify how Russia might intervene in Ukraine.
About 30,000 anti-government demonstrators seeking the ouster of President Yanukovych protested Sunday in Kyiv's barricaded Independence Square. It was one of the largest gatherings in two months of demonstrations against the Yanukovych government.
Mr. Yanukovych has accepted the resignation of his prime minister and revoked controversial anti-protest laws that angered demonstrators. But the protesters have demanded more concessions, including Mr. Yanukovych's resignation.