The embarrassing diplomatic incident comes as Ukraine's President Viktor Yanukovych was due to hold crisis talks with Russian counterpart and ally Vladimir Putin on the sidelines of the opening ceremony of the Winter Olympics in Sochi.
Washington and Brussels have engaged in a diplomatic standoff with Kiev and Moscow over mass protests that erupted in Ukraine in November when Yanukovych rejected a pact with the EU in favour of closer ties with former Soviet master Russia.
Washington's new top diplomat for Europe, Victoria Nuland, apologised yesterday for her comments.
"F*** the EU," Nuland says in what appeared to be a recent phone call with US ambassador to Kiev, Geoff Pyatt, which was somehow intercepted and uploaded onto YouTube accompanied by Russian captions.
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The US State Department was left fuming after the leak, pointing the finger at Russia for allegedly bugging the diplomats' phones.
"Certainly we think this is a new low in Russian tradecraft," said spokeswoman Jen Psaki, who did not dispute the authenticity of the call.
"That would be great I think to help glue this thing and have the UN glue it and you know, fuck the EU," Nuland says, in apparent frustration at policy differences.
The conversation appeared to have been held shortly after Yanukovych accepted his pro-Russian government's resignation on January 28.