It was not clear if this would harm Iran's drive to convince the UN watchdog International Atomic Energy Agency (IAEA) not to send it to the UN Security Council, which could impose punishing sanctions, for what the United States says is a covert nuclear weapons program.

The United States called on Britain, France and Germany, which had negotiated the enrichment freeze with Tehran, to send a "stern message" to Iran to stop producing the uranium feedstuff gas.

"We told the Europeans that we consider this to be really an act of bad faith and to deliver a stern message to Iran that they must stop this," an official said.

The US State Department had said earlier in Washington that if reports that Iran was making the uranium hexafluoride (UF6) gas that is the feed used to make enriched uranium proved to be true, it would further erode Tehran's already shaky credibility in nuclear matters.

Enriched uranium, made by spinning UF6 in what can be cascades of thousands of centrifuges, can be fuel for nuclear reactors or the raw explosive material for atomic bombs.

A total of "37 tonnes of uranium yellowcake ore have been introduced into Iran's uranium conversion facility in Isfahan and an unknown amount of UF6 has been produced," a Western diplomat said.

The comments were confirmed by other diplomats close to the IAEA, which has inspectors in Iran ready to verify the suspension of uranium enrichment that Tehran has said will begin Monday (November 22).

Iran had agreed last Sunday to suspend all uranium enrichment activities, in an accord worked out with EU negotiators Britain, France and Germany in order to keep Iran from being sent to the Security Council when the IAEA's 35-nation board of governors meets in Vienna next Thursday.

Iran claims its nuclear program is a strictly peaceful effort to produce electricity and agreed to a full enrichment suspension as a confidence-building measure.

A US official said Iranian nuclear negotiator Hossein Moussavian had told the European trio that Iran would not convert uranium into UF6 gas in the interval between reaching the agreement and its actually taking effect "but that verbal assurance meant nothing and this is clearly more bad faith by Iran."

"They've put it all in (the yellowcake in the Isfahan facility) and they think they have until November 22 to push it all through," said the Western diplomat.

A source close to the IAEA said Iran had almost decided to actually enrich some uranium before the November 22 deadline but had backed off from this due to the anger it would have caused in the international community.

"It could have been worse," the source said, referring to actual enrichment.

Iran has a 164-centrifuge cascade at a pilot plant but hundreds more centrifuges and the expertise to assemble and run them, analysts said.

The IAEA reported this month that Iran had said on October 14 that it had introduced 22.5 tonnes of yellowcake into the Isfahan facility but had not produced any UF6, news which reassured the agency.

But the total of 37 tonnes now in the conversion machines could produce a quantity of UF6 which would make about 100 kilograms (220 pounds) of HEU, enough for from four to six nuclear weapons.

Henry Sokolski, head of the Washington think tank the Nonproliferation Policy Education Center, said the Iranians were technically within their rights to make the uranium gas since the suspension starts Monday.

"This is humiliating to the Europeans but it's legal. What it shows is that the Iranians can run circles around the European negotiators," Sokolski said.

Under IAEA investigation since February 2003 for nuclear activities it had hidden for almost two decades, Iran agreed in October 2003 to suspend the actual enrichment of uranium.

Under international pressure for continuing to make centrifuges, Iran agreed in February 2004 to suspend such support activities but it said this did not include converting yellowcake into UF6, which is the first step in enrichment.

But even in agreeing to a full suspension, the Iranians stressed that this was a voluntary move.

The agreement with the European trio reaffirmed Iran's legal right under the nuclear Non-Proliferation Treaty (NPT) to enrich uranium for peaceful purposes.

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