Germany's Angela Merkel has said a US official's apparent insult of the EU's efforts to mediate in the Ukraine crisis is "totally unacceptable". Victoria Nuland has apologized after she referred disparagingly to the EU's role during a conversation said to be with the US ambassador to Ukraine. A recording of the exchange was posted online, with the US hinting at Russia's involvement in bugging and leaking it. The EU and US are involved in talks to end months of unrest in Ukraine. In Kiev, Ms Nuland - an assistant secretary of state - said she would not make a public statement on the matter. The state department said she had apologized in private to EU officials.