The Iranian president Mahmoud Ahmadinejad has fired the country's foreign minister Manouchehr Mottaki and temporarily replaced him with atomic chief Ali Akbar Salehi, the official IRNA news agency reported on Monday.
It gave no reasons for the surprise move, which comes as Iran is engaged in talks with world powers over its sensitive nuclear programme.
"I thank you and appreciate the work and the services you have rendered during your tenure in the foreign ministry," Ahmadinejad was quoted as saying in a directive carried by IRNA.
"I hope your efforts receive a praise by God and you will be successful in the rest of your life at the service of people of our Islamic nation," he added.
Mr Mottaki, a career diplomat, was appointed to the post of foreign minister in August 2005. He is currently in Senegal on an official visit.
A fluent speaker of English who is also comfortable in Urdu and Turkish, Mr Mottaki earned a degree in social sciences from the University of Bangalore in India and a graduate degree in international relations from Tehran University in 1991.
IRNA also said Mr Ahmadinejad, in a separate directive, appointed Ali Akbar Salehi as the "caretaker of the foreign ministry".
"Due to your commitment, knowledge and valued expertise ... you are appointed as caretaker of the foreign ministry," the directive read.
Mr Salehi is one of Iran's vice-presidents and head of its atomic energy organisation.
According to the law, the president has to submit his nominations for ministerial posts to parliament for approval.
The sacking of Mr Mottaki comes just days after Iran held crunch talks with world powers over its controversial nuclear dossier. Further talks are scheduled for next month.
Mr Mottaki, has been a staunch defender of Iran's sensitive nuclear programme, which Western powers suspect is masking a covert atomic weapons drive.
Iran maintains that it is seeking nuclear energy for peaceful purposes.
Earlier this month, while attending a security meeting in Bahrain, Mr Mottaki hailed as a "step forward" the US Secretary of State Hillary Clinton's remarks that Iran is entitled to a peaceful nuclear energy programme.
"But these words should be turned into action," he said in response to a question about comments to the BBC in which Mrs Clinton said Iran could enrich uranium for civilian purposes in future, but only after it had demonstrated it can do so responsibly.
Mr Salehi, who was appointed atomic energy chief in on July 17, 2009, has been a driving force behind Iran's atomic programme.
During his tenure, Iran's first nuclear power plant has come on line.
Mr Salehi also said earlier this month that Iran is now "self-sufficient" in the entire nuclear fuel cycle, and is able to supply itself with the raw material for fuel.
Mr Mottaki, between serving as diplomat to Ankara from 1985 to 1989 and later Tokyo from 1994 to 1998, headed the Western Europe section of the foreign ministry in 1989, and has also acted as a deputy FM and consultant between 1984 and 2004.
He was among those elected to the first parliament after Iran's Islamic Revolution in 1979.