The United States and European Union said they would lobby for Iran's referral to the UN Security Council at an emergency meeting of the UN atomic watchdog, the International Atomic Energy Agency (IAEA), set for February 2.

US Secretary of State Condoleezza Rice and EU foreign policy chief Javier Solana said the onus was on Iran to defuse mounting international concern over the nature of its nuclear project and dismissed Tehran's latest call for negotiations as disingenuous.

Rice said the message from Washington's European allies, which had been negotiating with Tehran, was "there is not much to talk about" after Iran moved to resume sensitive nuclear research last week.

"I think it's up to the Iranians to demonstrate that they are not just talking but they are serious," Rice told reporters before meeting with Solana at the State Department.

"It was the Iranians who walked away from the negotiations, who broke the moratorium (on nuclear activities)," Rice said of the effort led by Britain, France and Germany to resolve the crisis.

While diplomats predicted the 35-nation governing board of the IAEA would refer Iran to the Security Council for possible sanctions, Iran raised the stakes and said it would respond by blocking access to the agency's international inspectors.

Dr Ali Asghar Soltanieh, Iran's ambassador to the IAEA, said the UN monitoring agency's inspectors would no longer be allowed short-notice access to nuclear facilities and military sites if Tehran's activities were reported to the Security Council. In an interview on BBC News 24 television late Wednesday, Soltanieh was asked directly whether Iran would halt cooperation if the IAEA board votes for referral.

Echoing views by Iran's national security spokesman Hossein Entemazi, he replied: "I think that is clear...

"All the activities which we are voluntarily doing in accordance with additional protocols, including the complementary accesses (and) short notice access that we have granted... even to the military sites, will not be continued any more."

Iran agreed to an additional protocol in 2003 under the nuclear non-proliferation treaty, permitting more intrusive, snap inspections of its nuclear sites.