The United Nations' nuclear watchdog, the International Atomic Energy Agency (IAEA), has warned that Iran has passed a crucial nuclear threshold and could now go on to arm an atomic missile with relative ease.

In a report, the IAEA said that Iranian nuclear scientists had made at least 22 kilograms of enriched uranium of at least 20 per cent purity.

Experts estimate that 20 kilograms of uranium is the minimum required to arm a warhead, but Iran would still need to have its purity raised to 90 per cent.

Until February Iranians were enriching uranium to levels of no more than five per cent at its plant in Natanz.

"Iran's stockpile of low-enriched uranium, the feedstock of both civilian and military nuclear programmes, has risen by around 15 per cent since May to reach 2.8 tonnes. However the number of centrifuges that refine uranium to higher levels of purity has fallen to 3,772 from 3,936," The Telegraph quoted the report, as saying.

The agency's report comes in spite of the recent imposition at the UN of a fresh round of sanctions against Iran.

The prospect of an attack had receded only recently with American assurances that Tehran was more than a year away from acquiring a bomb.

The agency also rebuked the regime for its repeated failure to co-operate with weapons inspections designed to ensure that material was held securely at Iranian plants.

"The agency is ... concerned that the repeated objection to the designation of experienced inspectors hampers the inspection process and detracts from the agency's ability to implement safeguards in Iran," the report said.

The IAEA further alleged that some of its seals on Iran's stockpile of low enriched uranium (LEU) had been broken.

The seals are intended to ensure that Iran is not diverting LEU and secretly enriching it further to weapons-grade purity. (ANI)