Kiev: A top US envoy met on Thursday with members of Ukraine`s pro-EU opposition in the latest Western bid to end the country`s long-running crisis.
The visit came as a top Kremlin aide accused Washington of arming the opposition and hinted that Russia had legal grounds to intervene.
US Assistant Secretary of State Victoria Nuland was also due to hold talks today with President Viktor Yanukovych as a new attempt in parliament to agree a deal to curb presidential powers failed.
The US envoy and the opposition discussed possible changes to the constitution, said the party of jailed former prime minister Yulia Tymoshenko.
The new round of Western diplomacy comes in advance of expected talks between Yanukovych and Russian President Vladimir Putin on the sidelines of tomorrow`s opening ceremony of the Winter Olympic Games in the Black Sea resort of Sochi.
Putin`s economic aide in an interview published today accused Washington of financing and arming Ukrainian militants.
"According to our information, American sources spend USD 20 million a week on financing the opposition and rebels, including on weapons," Sergei Glazyev told the Ukrainian edition of Russia`s Kommersant.
"We have information that the militants are briefed on the territory of the US embassy, that they are being armed. Of course it is unacceptable," he said without providing further details.
The hawkish adviser, who is viewed as the Kremlin pointman on Ukraine, also argued that Russia had legal grounds for intervene in the crisis, citing the Budapest Memorandum on Security Assurances from 1994.
"According to this document, Russia and the United States are guarantors of Ukraine`s sovereignty and territorial integrity, and frankly speaking they are obliged to intervene when such conflicts arise."
The memorandum was signed after Ukraine demanded security guarantees in connection with its accession to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT).
The Kremlin has accused the West of trying to interfere in the domestic affairs of its Soviet-era satellite.
The protest movement has accused Yanukovych of dragging his feet in the crisis that began in November when Kiev rejected a historic EU trade and political association pact under Russian pressure.