The announcement followed talks between IAEA director general Mohamed ElBaradei and Iran's chief negotiator Ali Larijani, who arrived in Vienna unexpectedly on Sunday, IAEA spokeswoman Melissa Fleming said in a statement.

"Larijani invited the IAEA to send a team to Tehran to develop an action plan for resolving outstanding issues related to Iran's past nuclear programme," she said.

"The IAEA intends to send a team as early as practicable."

The mission, probably in July, will be headed by IAEA deputy director general Olli Heinonen, who is responsible for safeguard issues, according to a source in Vienna.

He is due this week to visit North Korea to prepare the closure of the plutonium production centre at Yongbyon.

In Tehran, the ISNA news agency reported that "the secretariat of Iran's national security supreme council, (headed by Ali Larijani) confirmed that IAEA inspectors are coming to Iran to develop an action plan for resolving outstanding issues related to Iran's past nuclear programme."

Larijani's second visit to Vienna in the space of 48 hours followed a meeting in Lisbon with European Union foreign policy chief Javier Solana, described by Solana as "very constructive".

On Friday, after meeting ElBaradei, Larijani had undertaken to define within two months an action plan with the IAEA, which is demanding the possibility of checking on the ground whether Iran's nuclear programme has military ambitions. The inspectors' mission is to "agree on how the action plan is going to take shape, details of it, and then implementation will start," a diplomat close to the IAEA told AFP.

"It was these outstanding issues surrounding the past nuclear programme that were the original reasons for the demands by the board and the (United Nations) Security Council for Iran to suspend (uranium enrichment)," he said.

"This is what started it all."

The announcement came as Britain and the United States are reportedly planning to put forward proposals at the UN Security Council to intensify two sets of existing sanctions targeting Iran's nuclear programme.

The new measures would include travel bans, the freezing of bank accounts and inspections of Iranian cargo ships and aircraft.

The West fears Iran's nuclear programme is aimed at producing nuclear weapons. Tehran insists that its ambitions are strictly peaceful, but stands accused of failing to fully cooperate with UN inspections.

Iran, which is a signatory of the Non-Proliferation Treaty, was placed under IAEA surveillance in 2003 after the disclosure of suspect secret activities.

In spite of demands from the UN Security Council Iran appears determined to press head with uranium enrichment.

A senior diplomat with ties to the IAEA said that Iran was already operating more than 1,300 centrifuges by mid-May at its Natanz plant and could have 3,000 by the end of July.

Under ideal conditions they could produce enough highly enriched uranium to produce a nuclear weapon within a year at most, the diplomat said.

"Probably if ElBaradei were to report positively, if he were able to say 'we're making progress on the issues' in his next report, the climate could also possibly change, and there would be a better chance for resumption of negotiation," the diplomat said.

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