A top US diplomat tried to play down the damage to Washington's diplomacy in Ukraine from a leaked telephone call on Friday, but German Chancellor Angela Merkel called an obscene remark about the EU "absolutely unacceptable."

US officials blamed Moscow for the Internet leak of recordings of Assistant Secretary of State Victoria Nuland and the US ambassador in Kiev discussing a possible future government for Ukraine, where Washington and Brussels back anti-Kremlin demonstrators.

On Friday Nuland tried to limit the diplomatic fall-out from her comment. "I am not going to comment on private diplomatic conversations. But it was pretty impressive tradecraft. The audio was extremely clear," she told reporters during a visit to Kiev.

She said she did not foresee damage to relations with opposition leaders, saying they "know exactly where we stand in respect of a non-violent solution to the problem."

Of relations with Russia, she said Washington and Moscow had "very deep, very broad and complex" discussions on a range of international issues including Iran and "frank and comradely discussions" on Ukraine.

Western officials described the leaks as a throwback to the cloak-and-dagger tactics of the Cold War, apparently aimed as much at sowing discord among Western allies as at discrediting the opposition in Ukraine, a country of 46 million people on the verge of bankruptcy, torn between East and West.

In the call, Nuland is heard using an expletive to tell the US ambassador to Ukraine, Geoffrey Pyatt, it would be better if a new Ukrainian government is backed by the United Nations than the EU," she says.

US officials did not deny the authenticity of the recording and said Nuland apologized to EU colleagues for the comment.

Angela Merkel, already furious with Washington for several months over reports that US officials bugged her own phone, found Nuland's remarks "totally unacceptable", a spokeswoman for the German chancellor said.

Merkel also expressed support for EU foreign policy chief Catherine Ashton, who heads the bloc's Ukraine policy.

In a separate leaked recording, an Ashton aide is overheard complaining about the United States for telling Ukrainian opposition members that Brussels was "soft" in its reluctance to impose measures such as sanctions to hurt the pro-Russian government.

Nuland met President Viktor Yanukovich in Kiev on Thursday before the Ukrainian leader flew off to meet President Vladimir Putin at the Olympics in Russia.-Reuters