The chief UN nuclear inspector said Saturday that a dialogue with Iran over its atomic programme was long overdue, as he prepared to depart for a visit to the Islamic republic.

"We are trying to resolve all the outstanding issues with Iran," International Atomic Energy Agency chief inspector Herman Nackaerts told reporters at Vienna airport.

"In particular we hope that Iran will engage with us on the possible military dimensions of Iran's nuclear programme. We are looking forward to the start of a dialogue, a dialogue that is overdue since very long."

Nackaerts was leading a six-person IAEA team that was due to hold talks with Iranian officials from Sunday until Tuesday. They were expected to arrive in Tehran in the early hours of Sunday morning.

The delegation also included IAEA number two Rafael Grossi, an Argentine, and the IAEA's senior legal official Peri Lynne Johnson, a US citizen, according to diplomats.

Nackaerts, who is Belgian, declined to comment on whom he would meet during the trip, which is aimed at clearing up what the IAEA called this week "outstanding substantive issues" on Tehran's nuclear programme.

Expectations are however low, with the delegation not expected to be given access to any sites mentioned in a damning IAEA report in November that raised suspicions Iran had done work developing nuclear weapons.

Iran's envoy to the IAEA, Ali Asghar Soltanieh, said on Tuesday that Tehran hoped the trip would "resolve any ambiguity and show (our) transparency and cooperation with the agency."

With Iran denying repeatedly that it wants nuclear weapons and dismissing the IAEA report as baseless, the watchdog's chief Yukiya Amano on Friday urged the Islamic republic to show "substantial cooperation" during the visit.

The report, which has led to a substantial increase in pressure on Iran from the United States, the European Union and others, detailed a string of areas in which it said Iranian activities were highly suspicious.

"We have information that indicates that Iran has engaged in activities relevant to the development of a nuclear explosive device," Amano said on Friday at the World Economic Forum in Davos, Switzerland.

"We are requesting that Iran clarifies the situation. We proposed to make a mission and they agreed to accept the mission. The preparations have gone well but we need to see what actually happens when the mission arrives."

Iran's President Mahmoud Ahmadinejad has insisted that Tehran is not dodging negotiations and was ready to sit down with world powers Britain, China, France, Russia, the United States, and Germany for talks.

The six powers are waiting for Tehran to reply to an October letter sent by EU foreign policy chief Catherine Ashton that stresses that discussions should focus on the "key question" of the Iranian nuclear issue.

Previous talks held a year ago in Istanbul ended without progress.

UN chief Ban Ki-moon, also in Davos, said that the onus was on Iran to prove its good intentions.

"There is no other alternative to addressing this crisis than peaceful resolution through dialogue," Ban told reporters.

"Iran should comply with the relevant Security Council resolutions. They have to prove themselves, that their nuclear development programme is genuinely for peaceful purposes which they have not done yet," Ban said.

What makes the international community all the more nervous is Tehran's continued defiance of UN Security Council resolutions calling on it to stop enriching uranium until the IAEA is satisfied its programme is peaceful.

Earlier this month the IAEA said Iran had begun enriching uranium to 20-percent purity deep inside a mountain bunker at Fordo, taking it significantly closer to the 90-percent mark needed for a nuclear bomb.