President Mahmoud Ahmadinejad gave no explanation for the change in a brief statement on his website. But the fired diplomat, Manouchehr Mottaki, is seen as close to Supreme Leader Ayatollah Ali Khamenei. And the president may be aiming to install a figure more personally loyal to himself as Tehran resumes critical talks with world powers over the nuclear program that has brought four rounds of U.N. sanctions on Iran.

The nuclear chief, Ali Akbar Salehi, is one of Ahmadinejad’s 12 vice presidents.

“This move 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.

Just a week before the shake-up, Iran resumed negotiations with six world powers over its suspect nuclear program after a long hiatus and another round is planned for early next year. Four sets of U.N. sanctions appear to be biting into the Iranian economy and Ahmadinejad may be looking for a loyal foreign minister who will help him clinch a deal with the six powers to ease the punitive measures.

A fourth round of sanctions was imposed in June over 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.

The sanctions are making it more difficult for Iran to trade with the outside world.

The president of Iran’s chamber of commerce, Mohammad Nahavandian, said last month that import prices for most goods have risen by 15 to 30 percent because of sanctions. That is because companies, particularly Asian firms, are bumping up prices because they know Iran is now a desperate market and insurance is difficult — if not impossible — to obtain on shipments to Iran.

And many European firms avoid dealings with Iran or their banks refrain from transactions with Iran.

Some of the tensions between Ahmadinejad and Mottaki have spilled out into public in this closely guarded nation.

In the past year, 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 the supreme leader. Khamenei has final say in all state matters in Iran, he runs the nuclear program and stands at the top of the clerical leadership that rules the country.

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

The difference was exposed in September when Mottaki publicly attacked Mohammad Baghaei, one of the four trusted foreign policy envoys appointed by Ahmadinejad, calling him an “inexperienced” figure who was “creating problems for the country’s foreign policy.” Mottaki overtly said that parallel foreign policy work must be avoided, a clear reference to Ahmadinejad appointees who operated outside the foreign ministry.

Ahmadinejad has challenged the supreme leader in the past over some political appointments. Last year, the president tried to resist Khamenei’s order that he fire one his vice presidents opposed by conservatives, though Ahmadinajed finally caved and removed him.

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.

It was not immediately clear how long Salehi — who holds a doctorate in nuclear physics from Massachusetts Institute of Technology in the U.S. — 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 fired as he 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.

The president thanked him for his more than five years of service — spanning Ahmadinejad’s entire time in office.

“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 the nuclear talks, which 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.”

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Murphy reported from Dubai, United Arab Emirates. Associated Press writer Slobodan Lekic in Brussels contributed to this report.