"It should come as no surprise that Iran has defied the board (of the IAEA) once again and announced it is producing uranium hexafluoride, the material for centrifuge enrichment," said Kurtis Cooper, a State Department spokesman.

"Although Iran has repeatedly asserted that its nuclear program is exclusively for peaceful purposes and its pursuit of uranium enrichment technologies are to fuel a planned civilian power program, Iran will have no peaceful use for enriched uranium for many, many years," he said.

"The rush to convert 37 tons of yellowcake into feed-stock for centrifuge enrichment has no peaceful justification," the spokesman said. "Iran has no operating nuclear power plants.

"Iran's urgent production of feed material for uranium enrichment clearly indicates Iran is continuing its unrelenting push toward nuclear weapons capability," he added.

"Thirty-seven tons of yellowcake is not a test. It is a production run," Cooper said. "It is enough uranium hexafluoride to feed a centrifuge enrichment process to produce highly enriched uranium in sufficient quantities for several nuclear weapons.

"Iran knows what it must do to alleviate international concern expressed by the IAEA on behalf of the international community. So far it appears determined to ignore the IAEA and proceed with its nuclear weapons program," he said.

A senior Iranian official said Tuesday that Iran has begun converting a large amount of uranium ore into the gas feed-stock needed to enrich uranium, in defiance of a UN call for it to fully suspend the sensitive process that can make material for nuclear weapons.

Iranian atomic energy chief Reza Aghazadeh told reporters in Vienna that some of the 37 tons of uranium yellowcake which Iran had previously said it would be converting had now been used.

Yellowcake is converted into uranium gas which is then fed into centrifuges to make enriched uranium. Enriched uranium can be fuel for civilian reactors, but also the explosive core for atomic bombs.

The IAEA, the UN nuclear watchdog, has urged Iran to "immediately" to suspend all parts of the nuclear fuel cycle, including conversion activities.

The agency set a deadline of November 25, when its board of governors will next be meeting, for a definitive review of Iran's nuclear program.

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