Helmut Metzner admitted acting as a mole for the US embassy during negotiations to form a government

The WikiLeaks revelations have claimed their first political scalp in Europe with the sacking of the German foreign minister's chief of staff, who acted as a mole for the Americans, keeping the US embassy in Berlin posted last year on the confidential negotiations to form Angela Merkel's new government.

Amid a mood of increasing anger in the German political class at the disparaging observations on the chancellor's cabinet from US officials, a liberal MP today demanded the withdrawal of the American ambassador in Berlin, Philip Murphy.

Guido Westerwelle, the German foreign minister and leader of the liberal Free Democrats, the junior partner in the Merkel coalition, is described unflatteringly in the US cables from Berlin as inexperienced, "exuberant" and "wild".

The cables relate how an FDP insider – "a fly on the wall, a young, up-and-coming party loyalist who was taking notes during the marathon talks" – delivered documents to the US embassy and kept US diplomats informed on the new government formation in October last year.

On Monday Westerwelle dismissed the reports as false and insisted there was no mole. But Helmut Metzner, his chief of staff, was sacked after admitting he was the source of the US intelligence.

"The staff member of the FDP's federal headquarters, who has admitted his contacts with the US embassy in Berlin, has been relieved of his duties as chief of staff for the FDP chairman," said a party statement.

Hans-Michael Goldmann, an FDP MP, told the Bildzeitung newspaper today that a German ambassador abroad behaving like Murphy would be promptly "called home". He added that Murphy had failed to apologise for the scandal.