Iran is now using domestically processed uranium in its nuclear programme, an Iranian diplomat said on Friday after some doubts were cast on his country's recent enrichment claims.

Iranian worshippers chant slogans in support of Iran's nuclear programme during Friday prayer ceremonies in Tehran, Iran May 19, 2006. [Reuters]

Iran said last month it had enriched uranium to the level used in power stations for the first time, crediting its own scientists for the breakthrough. The U.N. nuclear watchdog confirmed this from samples taken in Iran.

Iran's uranium conversion facility which makes UF6 is in Isfahan, a city south of the capital, while enrichment takes place at the nearby site of Natanz.

Iran said in April that its Isfahan plant had stockpiled 110 tonnes of feedstock UF6 gas.

Vienna diplomats have said Iran has had difficulty producing good quality UF6. In September the material was of such poor quality that it would have damaged the centrifuges -- machines that enrich uranium -- had it been used, they said.

A diplomat from the European Union accredited to the IAEA said Iran had probably chosen to use the better Chinese UF6 to hasten the process so President Mahmoud Ahmadinejdad could announce to the world without delay Iran's enrichment success.

Enrichment is a process of purifying uranium for use in nuclear power plants or, when very highly enriched, in bombs.

The European Union and United States believe Iran is secretly developing atomic weapons under cover of a civilian nuclear energy programme. Iran says its programme is solely aimed at the peaceful generation of electricity.

The IAEA has found no hard proof of any project to make atomic bombs but says that, after more than three years of probing, it still cannot confirm that Iran's intentions are entirely peaceful.

IAEA inspectors routinely visit Iran to monitor nuclear facilities but, after Iran's case was sent to the U.N. Security Council, Tehran stopped allowing unannounced inspections of sites at short notice.

A team of IAEA inspectors will arrive in Iran on Friday for one of their routine visits, state television reported.