International Atomic Energy Agency chief Yukiya Amano told AFP that the organisation's previous efforts to check Iran's claim its nuclear programme has only peaceful purposes had been hampered by "a lack of cooperation".

"We hope they will take a constructive approach. We hope that there will be substantial cooperation," Amano said.

An IAEA report in November highlighted a range of areas which had raised suspicions that Iran was pursuing the development of nuclear weapons, despite its repeated denials.

It detailed 12 suspicious areas such as testing explosives in a steel container at a military base and studies on Shahab-3 ballistic missile warheads.

Amano said it was too early to say definitively that Iran was pursuing a nuclear weapons programme.

But he added: "We have information that indicates that Iran has engaged in activities relevant to the development of a nuclear explosive device."

"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."

UN chief Ban Ki-moon said the onus was on Tehran to prove its good intentions to the inspectors, who will be visiting Iran from Sunday to Tuesday.

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

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.

"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.

Also in Davos, US Treasury Secretary Timothy Geithner said that more major countries, perhaps including China, were coming round to the idea of sanctions.

"China wants to be part of that effort. We're still at the early stage of the next wave of intensified financial pressure on oil and the financial side ... Europe has been excellent on this," he said.

"We are all engaged, it's an international effort ... trying ... to deter them from their nuclear ambitions. That's the most important thing."

China is a major importer of Iranian oil and has so far been reluctant to impose sanctions.

Instead, senior US officials said Tehran should formally reply to a letter offering talks, but specifying a condition that they focus on specific nuclear issues, sent by the European Union's foreign policy chief Catherine Ashton.

"Our position is that it is as it always has been -- the Iranian regime needs to live up to its obligations to the international community," White House spokesman Jay Carney told reporters aboard Air Force One.

"There is a process by which talks could take place. There is a letter out there from Lady Ashton that the Iranians could respond to."

State Department spokesman Victoria Nuland also said the Ashton letter provided the sole criteria for a resumption of dialogue.

"Just saying you're open for talks doesn't meet the criteria that we have set, which is to be ready for talks and ready to be serious about letting the world know all of the details of your nuclear program and proving your claims that it's for peaceful purposes."

Ahmadinejad said earlier that Iran, which is feeling the economic price of deepening international sanctions, would not be opposed to returning to the negotiating table.

"They have this excuse that Iran is dodging negotiations while it is not the case," he was quoted as saying by state media.

"A person who has logic and has right on his side, why should (he) refrain from negotiations?" Ahmadinejad asked rhetorically.

Ashton sent Iran's nuclear negotiator Saeed Jalili a letter in October on behalf of permanent UN Security Council members Britain, China, France, Russia and the United States, plus non-permanent member Germany.

It stated that "we can achieve a full settlement only by focusing on the key issue, which are the concerns about the nature of your nuclear program, as reflected in IAEA reports."

The last talks between the two sides took place in Istanbul a year ago and produced no results.

Since then, tensions over Iran's nuclear program, particularly between Washington and Tehran, have escalated dramatically.