"They are many years away from being able to convert enriched uranium into a bomb," Blix told the Ekot news program.

The United States and the European Union have repeatedly urged Iran to freeze uranium enrichment and reprocessing and to work with the UN atomic energy watchdog amid worries that Tehran is seeking to acquire nuclear weapons.

Tehran meanwhile has claimed that its nuclear program is for civilian use only.

News on Wednesday that Iran could within months take delivery of Russian nuclear fuel to fire up its first nuclear power station has exacerbated international concerns that the new Bushehr plant in southern Iran could be a cover for weapons development.

Blix on Thursday however said the concerns over that plant were exaggerated, pointing out that while the shell of the plant was built with German group Siemens before the Iran-Iraq war, Russia had stepped in after the war with only low-grade nuclear technology.

"It's like putting the motor of a Lada in a Mercedes car," he joked, adding that the light-water reactors being used are also not ideal for creating plutonium.

"It is possible, but it is very difficult. The way you would usually go is to have a research reactor," he said.

Although the Iranians have said they plan to build a 40 megawatt research reactor, Blix insisted that their plans are too far off to really cause much concern.

"What is uncomfortable and dangerous is that they have acquired the capacity to enrich uranium out of their own uranium that they dig out of the ground," he said, adding that it is hard to trust Tehran's claims that it will only enrich uranium to levels required for civil purpose.

"If you can enrich to five percent you can enrich it to 85 percent," he said.

Still, he said, the Iranians "have begun digging in the dirt a bit but they may need 10 years" for this to be a threat.

Blix, a former Swedish diplomat who was charged with searching for weapons of mass destruction in the 15 weeks leading up to the US-led invasion of Iraq in 2003, never hid his skepticism that Iraq actually had such weapons.

He currently heads an independent, international commission on weapons of mass destruction, which will work this year on finding ways of limiting the spread of nuclear, chemical and biological weapons, as well as on ways of disarming countries that already have such weapons.

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