"We are working to find out with our allies what the next course of action would be," spokeswoman Dana Perino said after the UN atomic watchdog reported it had been unable to make much progress in probing Tehran's nuclear drive.

Asked what impact the bitter feud between Washington and Moscow would have on securing fresh action in the UN Security Council where Russia has a veto power, Perino replied: "I take your point that things might be slightly more complicated now."

"But what I will tell you is that the action that Iran continues to take further isolates its people and its country from the rest of the international community. And I actually don't think that that has changed," she said.

Earlier, the International Atomic Energy Agency charged in a restricted report, a copy of which was seen by AFP, that Iran has not frozen uranium enrichment activities, which can be a key step towards nuclear weapons.

"This report shows once again that Iran is refusing to cooperate with the international community. The Iranian regime's continued defiance only further isolates the Iranian people," said White House spokesman Gordon Johndroe.

"We urge Iran to suspend its uranium enrichment and reprocessing activities or face further implementation of the existing United Nations Security Council sanctions and the possibility of new sanctions," said Johndroe.

The IAEA said in its report that it had "regrettably has not been able to make any substantive progress on the alleged studies and other associated key remaining issues which remain of serious concern."

Iran, under several sets of US and UN sanctions already, denies charges that its civilian nuclear program conceals a covert atomic weaopns drive, and has refused UN demands that it freeze its enrichment programs.

"On this particular issue, we've arrived at a gridlock," a senior official close to the IAEA told reporters, speaking on condition of anonymity.

The so-called "alleged studies" suggest Iran may have been trying to develop a nuclear warhead, convert uranium and test high explosives and a missile re-entry vehicle.

But Iran has so far done little to disprove the allegations, merely dismissing the documentation used to back them up as "forged" and "fabricated," the International Atomic Energy Agency said.

The report is to be discussed by the IAEA's board of governors next week.

IAEA Director General Mohamed ElBaradei "urges Iran to implement all measures required to build confidence in the exclusively peaceful nature of its nuclear program at the earliest possible date," the report concluded.

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