U.S. Assistant Secretary of State Victoria Nuland is refusing to comment on a leaked telephone conversation in which she used vulgar language about the European Union.
Nuland said Friday she will not talk about what she calls a "private diplomatic conversation," but said the recording was "impressive tradecraft" - a term referring to activity by intelligence agents.
In the call with U.S. Ambassador to Ukraine Geoffrey Pyatt, the Nuland voice uses foul language to suggest that the United States should ignore the European Union's position on resolving the crisis in Ukraine.
The State Department would not confirm or deny that the telephone call was genuine, but spokeswoman Jen Psaki said it does not reflect how Nuland feels about the EU. She said Nuland has been in close touch with EU officials on the situation in Ukraine.
U.S. officials have implied Russia may be involved in the leak, which was posted on the YouTube website.
U.S. officials on Thursday pointed to a tweet by an aide to Russian Deputy Prime Minister Dmitry Rogozin as the first to promote the recording.
In comments to the Associated Press, Rogozin's office denies involvement.
German Chancellor Angela Merkel calls Nuland's comments about the EU totally unacceptable. She also praised the work of EU foreign affairs chief Catherine Ashton, who has led the EU effort toward a settlement in Ukraine.