BERLIN (AFP) - German Chancellor Angela Merkel sees as "absolutely unacceptable" a top US diplomat's use of the f-word in commenting on the European Union's handling of the Ukraine crisis, her spokesman said on Friday.

"The chancellor considers this statement absolutely unacceptable ... and wants to emphasise again that (EU foreign policy chief Catherine) Ashton is doing an outstanding job," the spokesman said.

"The European Union will continue with its intensive efforts to calm the situation in Ukraine."

Washington's new top diplomat for Europe, Ms Victoria Nuland, apologised on Thursday for her comments.

In the recording, Ms Nuland and US ambassador to Kiev, Mr Geoff Pyatt, discussed frankly which opposition figures should go into the new Ukrainian government.

"That would be great I think to help glue this thing and have the UN glue it and you know, f*** the EU," Ms Nuland said, in apparent frustration at policy differences.

The clip went viral after somehow being intercepted and uploaded onto YouTube accompanied by Russian captions.

The US State Department was left fuming after the leak, pointing the finger at Russia for allegedly bugging the diplomats' phones.

Dr Merkel's spokesman Christiane Wirtz, asked whether a US apology had been received, told the Berlin press conference that "contact was made with the chancellery", without providing further details.

A German foreign ministry spokesman touched on the suspicion that Russia was behind the leak to take a swipe at the United States for its own sweeping surveillance, including allegedly of Dr Merkel's mobile phone.

"This shows you that eavesdropping is stupid," he said.

Washington and Brussels have engaged in a diplomatic standoff with Kiev and Moscow over mass protests that erupted in Ukraine in November when President Viktor Yanukovych rejected a pact with the EU in favour of closer ties with former Soviet master Russia.