After nine fruitless meetings with Iran over its alleged nuclear weapons research, the UN atomic agency may have to change approach, the US envoy to the IAEA said on Wednesday.

"Dialogue for the sake of dialogue is by its nature unproductive," Joseph Macmanus told reporters on the sidelines of an International Atomic Energy Agency meeting in Vienna.

"Since this has to be a productive process, if it is not and cannot be, then some adjustment might have to be made," he said.

"That is a consideration for the (IAEA) board in its regular meetings and also as an ongoing process. I think you will see and hear that taking place over the next several months."

The IAEA regularly inspects Iran's declared nuclear facilities but it also wants Tehran to address what it suspects are indications that the programme also has -- or at least had in the past -- "possible military dimensions" (PMD) aimed at developing the bomb.

Stretching back more than a year, the IAEA has held a series of failed meetings pressing Iran to address these allegations by giving the agency access to sites, documents and scientists, the latest last month.

Iran says the IAEA's claims, set out in a major report in November 2011, are based on information from Israeli and Western spy agencies -- information that it has not been shown -- and that it has never sought to develop nuclear weapons.

On Monday IAEA chief Yukiya Amano countered Iranian suggestions that the two sides had moved closer to a deal, saying he was "not aware of any progress."