VIENNA, Sept 21 (Reuters) - Iran has begun tests on a facility that will produce a large amount of material for nuclear centrifuges, a top Iranian nuclear official said on Tuesday.

Gholamreza Aghazadeh, the head of Iran's Atomic Energy Organisation, told reporters in Vienna Iran had begun converting 37 tonnes of raw uranium into material which is fuel for nuclear centrifuges -- the machines that enrich uranium.

One nuclear expert has said that, if enriched, that would be enough material for five nuclear weapons.

"Some of the amount of the 37 tonnes has been used. The tests have been successful but these tests have to be continued using the rest of the material," said Aghazadeh, who is attending a general conference of the Vienna-based U.N. nuclear watchdog, the International Atomic Energy Agency (IAEA).

Iran had told the IAEA a few weeks ago it intended to run the tests. However, the announcement came after the IAEA board of governors passed a resolution on Saturday calling on Iran to halt all activities linked to uranium enrichment.