The head of the UN atomic agency reached out Monday to Iran's new government but said Tehran must urgently do more to remove suspicions it wants nuclear weapons.

The International Atomic Energy Agency "remains committed to working constructively with Iran, under the country's new government, to resolve outstanding issues by diplomatic means," Yukiya Amano told a meeting of the IAEA's board of governors.

He added however: "Given the nature and extent of credible information available to the agency about possible military dimensions to Iran's nuclear programme, it remains essential and urgent for Iran to engage with us on the substance of these concerns."

He reiterated the IAEA's long-standing statement that since Iran is not providing the necessary cooperation it "cannot conclude" that all its nuclear work is peaceful, according to the text of his remarks.

It is because of this that the UN Security Council has passed six resolutions since 2006 -- four with sanctions attached -- calling for Tehran to suspend key parts of its nuclear work.

Denying it wants nuclear weapons, Iran has instead defiantly continued to expand its programme, most notably in the enrichment of uranium, which in highly purified form could be used in a bomb.

The United States and Israel, the Middle East's sole if undeclared country with nuclear weapons, have refused to rule out military means to stop Tehran's nuclear drive.

Numerous diplomatic initiatives over the past decade to find a peaceful solution have failed, and all the while Iran has moved closer -- in theory -- to being able to have atomic weapons.

Conciliatory-sounding noises from Hassan Rowhani since his election as president in June, replacing the more hardline Mahmoud Ahmadinejad, has however created some hope.

Himself a former nuclear negotiator, Rowhani has handed responsibility for future talks to the foreign ministry under the US-educated moderate Mohammad Javad Zarif.

A new round of talks between Iran and the IAEA is set for September 27, and a meeting with the five permanent members of the UN Security Council plus Germany (the P5+1 or E3+3), the first since April, is expected soon.

Zarif said on Friday after a phone call with EU foreign policy chief Catherine Ashton, P5+1 lead negotiator, that Tehran wanted to "remove any ambiguity" about its nuclear work.

The two will meet during the UN General Assembly later this month.

Rowhani has also appointed a new Iranian envoy to the IAEA, Reza Najafi, and former foreign minister Ali Akbar Salehi as head of Iran's Atomic Energy Organisation.

Salehi indicated last week that Iran could grant the IAEA greater inspection rights.

The P5+1 powers usually use the quarterly IAEA meetings to take Iran to task, but this time they are holding off in order to see whether progress really can be made with Rowhani.

Amano told a news conference Monday it was "too early to speculate" what the effect of having a new government in Iran will be.

Looming large in the background however is the desire of US President Barack Obama to bomb Iran's ally Syria over the latter's alleged use of chemical weapons on August 21.

Zarif said on Sunday in Iraq that such a strike would be "illegal" and Tehran has backed claims that rebels were behind the attack, which killed hundreds of people.

Russia, which opposes military action on Syria, has warned of "catastrophic" consequences if a small nuclear research reactor in the Damascus suburbs were hit.

Moscow raised the issue Monday at the IAEA meeting and has requested a risk analysis from the agency.

The US ambassador to the IAEA said however that such a "highly speculative investigation" was not within UN agency's legal mandate, according to the text of his remarks seen by AFP.

Amano told reporters the IAEA was considering the Russian request but that the reactor contained around one kilo (two pounds) of highly-enriched uranium, calling this "not a big amount".