Initial reports gave no reason for Mahmoud Ahmadinejad's decision. There had been no indication that Mr Mottaki, a key figure in Iran's nuclear negotiations with the West, was about to lose his job.

Mr Ahmadinejad has appointed the country's top nuclear official, Ali Akbar Salehi, to replace Mr Mottaki in a caretaker capacity.

"I appreciate your diligence and services as the foreign minister," said Mr Ahmadinejad in a letter to Mr Mottaki, Mehr news agency reported.

Analysts say Mr Mottaki's dismissal may be part of a political power play among ruling conservatives in Iran.

There has been mutual distrust between the president and Mr Mottaki since the 2005 election that brought Mr Ahmadinejad to power: Mr Mottaki was the campaign manager for one of Mr Ahmadinejad's rivals, Ali Larijani.

Mr Mottaki, who is currently in Senegal on an official visit, was appointed foreign minister in 2005.