Government spokesman Gholam Hossein Elham said Larijani had already offered his resignation several times and now President Mahmoud Ahmadinejad had chosen to accept it.

"Larijani had resigned several times and finally the president accepted his resignation," state news agency IRNA quoted Elham as saying. "The appointment of Larijani's replacement is under study."

Rumours have been circulating in Iran for months that Larijani was unhappy and had offered to resign several times. But nothing had ever been confirmed by officials.

Elham offered no explanation for the resignation except to say that Larijani had "personal reasons" to step down.

"He said he wanted to have other activities in politics and had asked the president several times to resign from his post," he said, according to the Fars news agency.

Larijani, who took on his post after Ahmadinejad's election in 2005, was one of the most powerful figures in the Islamic republic, leading two years of sensitive talks with EU officials over Iran's nuclear programme.

He maintained Iran's position that it would never yield in the nuclear standoff.

In his capacity as head of the Supreme National Security Council, he also handled other security issues, including the process leading up to the release of 15 British sailors arrested in Iran in March.

Iran is expected to appoint a deputy foreign minister, Saeed Jalili, to replace Larijani, the Iranian media reported.

Elham added that Iran's next meeting with EU foreign policy chief Javier Solana, scheduled for Tuesday in Rome, would go ahead with Larijani's successor.

It will take place "as scheduled with the new head of supreme national security council," he said.

Iranian media however said it was still possible that Larijani would take part in the meeting in some capacity.

The resignation also came after confusion of whether Russian President Vladimir Putin had handed over a message on Iran's nuclear programme during his landmark visit to Iran last week.

Larijani had said on Wednesday that Putin made a special proposal to break the deadlock over the nuclear programme in talks with supreme leader Ayatollah Ali Khamenei during his visit to Iran on Tuesday.

But Ahmadinejad was quoted as saying by the semi-official Fars news agency: "There was no nuclear proposal."

Ahmadinejad did not explain his contradiction of the remarks by Larijani, who is also an ex-head of state broadcasting.

Despite several meetings during the past year, Larijani and Solana have not overcome the deadlock over Tehran's refusal to suspend its sensitive uranium enrichment activities.

Solana must report to major world powers Britain, France, Germany, Russia, China and the United States before mid-November on Iran's willingness to give up uranium enrichment in exchange for political and trade incentives.

The West, led by the United States, believes that Iran's nuclear programme is cover for a drive to develop an atomic bomb, but Tehran insists it is for civilian objectives only.

The UN Security Council has already imposed two sets of sanctions on Iran over its refusal to suspend uranium enrichment activities, a process that can be used both to make atomic fuel and in highly enriched form a nuclear weapon.

Frustrated by the slow pace in agreeing more UN sanctions, the United States and European allies like France are also pushing for unilateral action to step up the economic pressure on Iran.

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