"I officially announce that Iran has joined countries with nuclear technology," Mr Ahmadinejad said. He stressed that Iran's nuclear efforts were for peaceful purpose and that no country should stand in its way.

The enrichment took place on April 10, the president said, adding that "our nuclear activities have been under complete supervision, unprecedented supervisions" by the International Atomic Energy Agency.

"And today we are interested in operating under IAEA supervision," he said.

Earlier on Tuesday, Gholamreza Aghazadeh, head of Iran's atomic energy agency, said that the Natanz facility had enriched uranium at 3.5 percent - a low-grade level sufficient to run a power plant, but far below the 90 percent required for weapons.

The UN Security Council has demanded that Iran cease its enrichment activities, but Tehran says that the country has a right to produce nuclear fuel for peaceful purposes.

IAEA Director-General Mohammed ElBaradei plans to visit Iran this week.