As hours ticked down to the deadline, the US secretary of state warned bluntly that the UN Security Council "has to act" to maintain its credibility in the face of the hardline Tehran regime's intransigeance.

"In order to be credible the Security Council of course has to act," Rice told reporters on the sidelines of talks with her NATO counterparts in Sofia, in a clear reference to possible sanctions.

Demonstrating attempts to present a united front on the issue, France's Foreign Minister Philippe Douste-Blazy echoed the US call, urging the Security Council to send a "rapid and firm" signal to Iran.

"The situation is serious and worrying," Douste-Blazy said, adding: "There is nothing to suggest that Iran is conforming to the demands of the international community."

Western powers, led by the United States, allege Iran is trying to develop a nuclear missile capability but Iran insists it is developing nuclear technology only to produce atomic energy.

Washington has backed tough action but Moscow and Beijing, also permanent members of the Security Council, have called for continued negotiation through the UN nuclear watchdog, the International Atomic Energy Agency (IAEA).

Russian Foreign Minister Sergei Lavrov was due to brief his NATO colleagues on Moscow's latest thinking at the Sofia talks, which came hours before IAEA boss Mohamed ElBaradei was due to present a crunch report in Vienna.

The two sides were likely to play down differences, but observers were watching closely for signs of diplomatic movement.

The two-day NATO talks in Bulgaria, in theory focused on Sudan's Darfur crisis, Afghanistan and NATO enlargement, have been overshadowed by the Iran standoff.

While not formally on the NATO agenda, Iran was on the menu at a so-called "transatlantic dinner" Thursday evening which gathered the NATO ministers with their European Union colleagues and EU foreign policy chief Javier Solana.

Officials were tightlipped afterwards. "There was a sense of commitment to unity," said one US official, declining to comment further.

Earlier Thursday Iran's hardline President Mahmoud Ahmadinejad vowed that his country "will not bow to injustice and pressure."

"Thanks to God, we are a nuclear state. We want peace and security and we are not a threat to anyone. We are ready for dialogue on disarming the big powers in order to reinforce peace and security," he added.

German Foreign Minister Frank-Walter Steinmeier also addressed the Iran crisis on the sidelines of the Sofia meeting.

"We expect it (Iran) to meet international standards and... to allay world suspicions that its civil nuclear operations are being used to develop a possible weapons program."

Security is tight for the Sofia talks, with some 3,000 police officers on the streets and around the National Palace of Culture, hosting the meeting.

About 1,000 nationalist protestors rallied in Sofia against the visit by the US secretary of state, who is to sign accords to set up three military bases in Bulgaria, brandishing banners including one reading: "Yankees Go Home".

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