ElBaradei is expected to meet officials including President Mahmoud Ahmadinejad, Iran's atomic energy organisation chief Gholam Reza Aghazadeh, and possibly supreme leader Ayatollah Ali Khamenei.

His visit comes amid talks between the International Atomic Energy Agency (IAEA) and Iran aimed at resolving questions over the history of the Iranian nuclear programme, which the West fears could be diverted to weapons use.

Accompanied by IAEA deputy director general Olli Heinonen, ElBaradei declined to make any comment on arriving in Tehran, dismissing questions with a wave of the hand, an AFP correspondent reported.

He hopes the visit will help in "resolving all remaining outstanding issues and enabling the agency to provide assurance about Iran's past and present nuclear activities," IAEA spokeswoman Melissa Fleming said this week.

Despite a four year probe into Tehran's atomic drive, the IAEA has never been unable to confirm whether the programme is peaceful. But it has also found no evidence to back Western claims Iran has sought atomic weapons.

A recent US intelligence report said Iran halted a nuclear weapons programme in 2003, undermining repeated accusations from US President George W. Bush that Tehran was actively seeking the atomic bomb.

The report appears to have momentarily taken the heat out of the atomic crisis but Washington still wants UN Security Council to adopt a third set of sanctions against Tehran over its nuclear programme.

The UN Security Council has repeatedly called on Iran to freeze the sensitive process of uranium enrichment -- which can be used both to make atomic fuel and a bomb.

But Iran has repeatedly said it has every right to the full nuclear fuel cycle and insists its nuclear programme is solely aimed at generating electricity for a population whose fossil fuels will eventually run out.

Bush, speaking on his first visit as US president to Iran's arch regional foe Israel, underlined his belief that Tehran remained a threat to world security.

"Iran was a threat, Iran is a threat and Iran will be threat to world peace if the international community does not come together and prevent that nation from the development of the know-how to build a nuclear weapon," said Bush.

"A country that once had a secret programme can easily restart a secret programme. A country which can enrich (uranium) for civilian purposes can easily transfer that knowledge to a military programme," said Bush.

Although tensions between Iran and the United States appeared to have lessened after the intelligence report, the enmity between the foes was made clear when Washington accused Tehran of harassing its ships at the weekend.

The Pentagon said Iranian Revolutionary Guards threatened to blow up US warships they encountered in the Strait of Hormuz but Tehran insisted the meeting at sea was routine.

Iran and the IAEA on Tuesday wrapped up the latest chapter in their talks -- uranium particle contamination found in the past by UN inspectors at the technical college of Tehran University.

The two sides have already held discussions about Iran's past experiments with plutonium and its use of uranium-enriching P1 and P2 centrifuges.

The talks are in line with a timetable agreed by both sides in August for Tehran to provide more information over various areas of ambiguity in its nuclear programme.

Iran has said its stepped up cooperation with the IAEA should mean it avoids further sanctions although the United States has expressed suspicion about Tehran's motives in the talks.

ElBaradei has previously made five trips to Iran since the nuclear standoff between the Islamic Republic and the international community began in 2002. However his last dates back to April 2006.

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