Argentine Foreign Minister Jorge Taiana has unexpectedly resigned after more than four years in the post.
Mr Taiana said he had handed in his resignation after a telephone call to President Cristina Fernandez de Kirchner.
He cited personal reasons, but analysts say he and the president have recently clashed over foreign policy.
He will be replaced by Hector Timerman, the current ambassador to the US.
Mr Taiana became foreign minister in December 2005, during the presidency of Nestor Kirchner - the husband of the current president.
Mr Taiana had been a close ally of both Mr and Mrs Kirchner, but analysts told BBC Mundo the couple's strong influence over foreign policy may have alienated the foreign minister.
Mr Timerman, 56, is a former journalist who co-founded the human rights organisation Americas Watch.