But White House press secretary Jay Carney also did not deny the conversation took place.
U.S. President Barack Obama's top diplomat to Europe apparently dropped the F-bomb in a conversation on the European Union and Ukraine, captured on YouTube.
Asked by a reporter whether the conversation was "real," Carney said: "I think the State Department obviously is aware of it. You know, we don't discuss private diplomatic conversations. It's certainly no secret that our ambassador and assistant secretary have been working with the government of Ukraine, with the opposition, with business and civil society leaders to support their efforts to find a peaceful solution through dialogue and political and economic reform."
Carney referred further questions to the U.S. State Department.
The conversation between Assistant Secretary of State Victoria Nuland and U.S. Ambassador to Ukraine Geoffrey Pyatt was leaked anonymously to YouTube, the Hill reported. Russian involvement is suspected.
The newspaper said Nuland and Pyatt are not identified on the recording, but it appears to be genuine and the U.S. State Department has not issued a denial.
The leaked telephone call was first reported by Ukraine's Kiev Post. In it, Nuland sharply criticizes the EU's handling of the Ukraine crisis.
The Hill said Nuland's criticism was in the context of praising U.N. Secretary-General Ban Ki-moon for choosing an envoy to deal with the political crisis.
In the tape, Nuland said the U.N. envoy will "help glue this thing and to have the U.N. glue it. And you know, [expletive] the EU."
"Exactly," Pyatt can be heard replying, the Hill reported. "And I think we got to do something to make it stick together, because you can be sure that if it does start to gain altitude the Russians will be working behind the scenes to torpedo it."
The report did not say when the conversation was recorded.