The UN nuclear watchdog chief began talks in Tehran on Monday, Iranian media said, after voicing hope for a deal to investigate suspected atomic bomb research - a possible breakthrough that Iran may count on to ease sanctions and deflect threats of war.

International Atomic Energy Agency Director-General Yukiya Amano met the head of Iran's nuclear energy organisation, Fereydoun Abbasi-Davani, hours after his pre-dawn arrival, according to ISNA news agency.

Amano, who was on his first trip to Iran since taking office in 2009, a period marked by rising tension between the IAEA and Tehran, was also due to meet Iran's chief nuclear negotiator, Saeed Jalili and Foreign Minister Ali Akbar Salehi on Monday. He was greeted at Tehran airport by Iran's IAEA ambassador.

'I really think this is the right time to reach agreement.
Nothing is certain but I stay positive,' Amano, a veteran Japanese diplomat with long experience in nuclear proliferation and disarmament affairs, said before departure from Vienna airport. He added that 'good progress' had already been made.

But while Amano scheduled Monday's talks with Iran at such short notice that diplomats said agreement on improved IAEA access in Iran seemed near, few see Tehran convincing Western governments to ease back swiftly on punitive sanctions when its negotiators meet global power envoys in Baghdad on Wednesday.

Two days after seeing Amano, Jalili will hold talks in the Iraqi capital with Catherine Ashton, the European Union foreign policy chief heading a six-power coalition comprised of the five U.N. Security Council permanent members plus Germany.

By promising extended cooperation with U.N. inspectors, diplomats say Iran might aim for leverage going into the broader negotiations where the United States and its allies want Iran to  curb works they say are a cover for developing nuclear weapons.

Intensifying Western sanctions on Iran's energy exports, and threats by Israel and Washington of military action, have pushed up world oil prices, compounding economic misery wrought by debt crises in many industrialised countries. 

Some Western diplomats said Amano, given a recent history of strained relations with Iran, would pay a rare visit to Tehran only if he believed a framework agreement to give his inspectors freer hands in their investigation was close. Iran has been stonewalling IAEA requests for better access since 2008.

'Either they (IAEA) are very sure that they have an agreement or he is simply upping the ante to get an agreement, he is going in at the highest level the agency can. (But) with Iran nothing is ever in the bag,' said a European diplomat. 'We regard the visit ... as a gesture of goodwill,' Salehi said.

He hoped for agreement on a 'new modality' to work with the IAEA that would 'help clear up the ambiguities'.

The UN watchdog is seeking access to sites, nuclear officials and scientists and documents to shed light on work in Iran applicable to developing the capability to make nuclear weapons, especially the Parchin military complex outside Tehran.

Two meetings between Iran and senior Amano aides in Tehran in January and February failed to make any notable progress. But both sides were more upbeat after another round of talks in Vienna last week, raising hopes for a deal.

'We need to keep up the momentum. There has been good progress during the recent round of discussions between Iran and the IAEA,' Amano said, adding he did not expect to visit Parchin during his short, one-day stay in Tehran.

Yet while an Iranian agreement on a so-called 'structured approach' outlining the ground rules on how to address the IAEA's questions would be welcome, it remains to be seen how and when it will be implemented in practice.

'We'll see if the Iranians agree to let the agency visit Parchin. I have my doubts, no matter what any agreement says on paper,' said one Western envoy ahead of Amano's visit to Iran and the meeting with world powers, the P5+1, in Baghdad.

Such a deal would also not be enough in itself to allay international concerns. World powers want Iran to curb uranium enrichment, which can yield fuel for nuclear power plants or for nuclear bombs, depending on the level of refinement.

Iran, to general disbelief from its Israeli and Western adversaries, insists its nuclear programme is intended only to generate electricity and produce isotopes for cancer treatment. Unlike its arch-enemy Israel, assumed to harbour the Middle East's only nuclear arsenal, Iran is a signatory to treaties that oblige it to be transparent with the IAEA.

 'We are not going to do anything concrete in exchange for nice words,' another diplomat said of the Baghdad meeting, the outcome of a big power meeting with Iran in Istanbul last month that ended a diplomatic freeze of more than a year.

'Presumably, we will get a flavour of what the Iranians are prepared to do,' the diplomat said. 'It sounds like they are interested in making progress.'

Another said: 'What we need now, with the situation in the region, are urgently concrete steps. So our talks will focus on something that can be implemented very quickly.'

An adviser to Iran's Supreme Leader Ayatollah Ali Khamenei said there were hopes the Baghdad meeting would be successful. But Iran will not 'tolerate any pressure and it decides about its destiny in the nuclear issue with full authority,' Mehr News Agency quoted Ali Akbar Velayati as saying.

The IAEA wants Iran to address issues raised by an agency report last year that revealed intelligence pointing to past and possibly ongoing activity to help develop nuclear explosives.

Iran says the intelligence is fabricated, and has so far resisted requests for inspectors to visit Parchin.-Reuters