Coming from Iranian Vice President Gholam Reza Aghazadeh, the announcement compounded international scepticism about denting Tehran's nuclear defiance just five days after Tehran stonewalled demands from six world powers to suspend activities that can produce the fissile core of warheads.

Besides demanding a stop to uranium enrichment - which can create both fuel and the nuclear missile payloads - the international community has also been pressuring Tehran to co-operate with the IAEA in its probe of allegations that Tehran hid attempts to make nuclear arms.

That investigation was launched a year ago under a so-called "work plan" between the Vienna-based agency and Tehran.

Back then, IAEA chief Mohamed ElBaradei hailed it as "a significant step forward" that - if honoured by Iran - would fill in the missing pieces of Iran's nuclear jigsaw puzzle; nearly two decades of atomic work, all of it clandestine until revealed by dissidents nearly six years ago.

And he brushed aside suggestions that Iran was using the work plan as a smoke screen to deflect attention away from its continued defiance of a UN Security Council ban on enrichment.

But the plan ran into trouble just months after it was put into operation. Deadline after deadline was extended because of Iranian foot-dragging. The probe, originally to have been completed late last year, spilled into the first months of 2008, and then beyond.

Iran remains defiant, saying evidence from the US and other board members purportedly backing the allegations was fabricated, and Aghazadeh appeared to signal that his country was no longer prepared even to discuss the issue with the Vienna-based IAEA.

Investigating such allegations "is outside the domain of the agency," he said. Any further queries on the issue "will be dealt with in another way," he added, without going into detail.

Britain, one of the main critics of Iran's nuclear activities, was critical. "We are concerned by reports that Iran is refusing to co-operate with the IAEA on allegations over nuclear weapons," a spokesman for the Foreign Office said.