Updated

TEHRAN, Iran -- Iranian President Mahmoud Ahmadinejad abruptly fired his foreign minister Monday as he was in the middle of an official visit to Africa and named the nuclear chief as the acting top diplomat.

The president thanked Manouchehr Mottaki for his more than five years of service -- spanning Ahmadinejad's entire time in office -- but gave no explanation for the change in a brief statement on his website. He named nuclear chief Ali Akbar Salehi, who is also one of the country's 12 vice presidents, to serve as caretaker foreign minister.

The sudden shake-up could reflect growing rifts between the ruling clerics and Ahmadinejad's hard-line government, which is strongly backed by the powerful Revolutionary Guard.

"This moves shows not only the internal tensions but the primacy of the nuclear issue as Iran's main foreign policy objective," said Rasool Nafisi, an expert on Iranian affairs at Strayer University in Virginia.

A fourth round of sanctions was imposed in June in response to Iran's refusal to halt uranium enrichment, a key part of its nuclear program that is of international concern because it can be used both for making reactor fuel and atomic weapons. Iran insists its aims are entirely peaceful, but the U.N.'s International Atomic Energy Agency says its years of investigating have not been able to confirm that.

In the past year, there were reports that Mottaki opposed a decision by Ahmadinejad to appoint his own special foreign envoys to key areas such as the Middle East, Afghanistan and the Caspian Sea region. Mottaki found the appointments embarrassing to the foreign ministry and allegedly took his complaint to Supreme Leader Ayatollah Ali Khamenei, who has the final say on all state matters.

Khamenei reportedly sided with Mottaki, forcing Ahmadinejad to moderate his position and change their title only to the level of advisers.

Iranian media have also reported in the past year that some lawmakers were pushing for Mottaki to be dismissed, arguing that he failed to adequately defend Iran at international organizations such as the United Nations. Iran is scheduled to hold another round of talks with world powers early next year over its disputed nuclear program.

It was not immediately clear how long Salehi would remain in the caretaker role. The semiofficial Fars news agency says Mohammad Ghannadi, a prominent nuclear scientist, is expected to replace Salehi as the new nuclear chief -- an indication Ahmadinejad wants him to keep the job permanently. Ghannadi is currently Salehi's deputy at the Atomic Energy Organization of Iran.
Salehi -- or any other candidate -- has to win a vote of confidence from the 290-seat parliament to be appointed to the job.

Prominent conservative lawmaker Alaeddin Boroujerdi says he was stunned to hear the news, saying the parliament was not aware of Ahmadinejad's decision to dismiss Mottaki, according to khabaronline.ir news website.

Mottaki was in the middle of a tour of African nations that took him to Senegal, where he delivered a message from Ahmadinejad to the West African nation's president on Monday, according to the official IRNA news agency.

"It's unpleasant that he is fired in the middle of a foreign assignment. The president should have waited for Mottaki to return home first before a replacement," said conservative lawmaker Mahmoud Ahmadi Biqash.

German Foreign Minister Guido Westerwelle said Mottaki's dismissal should not affect negotiations between Iran and six world powers, adding that the process -- which resumed last week in Geneva -- should continue regardless of the officials involved.

The next round of talks between Iran and the six permanent U.N. Security Council members -- the U.S., Britain, France, Germany, Russia and China -- and Germany is scheduled for January.

"We put emphasis that talks which just started in Geneva will continue and that different political constellations in Iran will not lead to any disruptions or delay in the talks," Westerwelle said in Brussels, where he is attending a meeting of EU foreign ministers.

Talks between Iran and the world powers broke down last year when Iran rebuffed a U.N.-drafted plan to ship abroad its stockpile of low-enriched uranium in exchange for reactor-ready fuel. Low-enriched uranium can be used in reactors, but also for warheads if brought to much higher enrichment levels.

Earlier this month, Mottaki attended a security conference in Bahrain that included U.S. Secretary of State Hillary Rodham Clinton. Mottaki, however, was on the defensive after American diplomatic memos released by WikiLeaks showed some Gulf Arab leaders urging for a U.S. military strike to cripple Iran's nuclear program.

He tried to reassure Gulf Arab nations that Iran was not a regional threat, but his statements did not resonate, said Salman Shaikh, director of The Brookings Doha Center in Qatar.

"He had a golden opportunity to change some minds about Iran, but failed," said Shaikh. "This showed that Iranian foreign policy was stumbling and perhaps this led to the change."