A European diplomat told AFP news service that Iran had received a letter from Britain, France and Germany warning of "consequences if they restart conversion activities."

The letter also "proposes a four-way meeting in the near future.

"We hope the Iranians will reconsider," one diplomat said, adding that the letter was delivered to Iran on Tuesday or Wednesday.

France urged Iran to think again and to maintain negotiations.

"We reaffirm our attachment to the Paris agreement of November 2004, which envisages the suspension of activities linked to the enrichment and treatment (of uranium) ... and we call for more discussions," the foreign ministry said in Paris.

Blair would support Security Council action

Britain would back UN Security Council action against Iran if the country breaks it pledges over its nuclear program, Prime Minister Tony Blair said Thursday.

"Let's wait and see what actually happens," Blair said at a press conference when quizzed about a response to Iran's threats. "But we certainly will support referral to the UN Security Council if Iran breaches its undertakings and obligations. Quite how that will come about we have got to work out with our colleagues and allies. But those international rules are there for a reason, and they have to be adhered to."

A top Iranian nuclear official had said earlier Thursday the country could soon announce the resumption of "a noticeable part" of uranium conversion work, a precursor to uranium enrichment.

Tehran no longer respects treaty

And Iran's Isna agency quoted Hassan Rowhani, the Islamic republic's top nuclear negotiator, as saying Tehran would "no longer have any respect" for the nuclear Non-Proliferation Treaty (NPT) if it was prevented from using atomic technology and the full nuclear cycle for peaceful purposes.

Iran's enrichment program is the focus of international fears that the clerical regime is seeking to develop nuclear weapons. Iran insists it only wants to make atomic energy reactor fuel.

But the watchdog International Atomic Energy Agency (IAEA) said it hoped intense last-minute talks with Iran would dissuade Tehran.

"I know there was a lot of diplomacy last night," a Western diplomat said on customary condition of anonymity.

Ongoing discussions

Top Iranian negotiator Cyrus Nasseri told AFP by telephone from Vienna that "discussions" were ongoing.

Iran agreed in the November deal with European Union members Britain, France and Germany to suspend its uranium enrichment work, including conversion, as a "confidence building" gesture.

The diplomat said it was not certain that the IAEA would receive a letter from Iran announcing the resumption of the work on Thursday.

The source pointed at a report in the Washington Post that Iranian officials had decided to hold off on notifying the Vienna-based IAEA and were considering an offer to restart talks in

the next two weeks.

According to that report, the three EU countries have notified Tehran that they will abandon talks and support a US strategy for punitive measures against Iran if it resumes the nuclear activity.

Russia will continue cooperating with Iran

A Russian nuclear official said Iran's intention to restart the sensitive activities was "legitimate" and would not alter Russia's nuclear cooperation with the Islamic state.

"The fact that Iran has restarted conversion will not have an impact on nuclear cooperation between Russia and Iran," said the official, speaking to AFP on condition of anonymity.

"This does not threaten international security because this uranium will be used for peaceful ends and under the strict IAEA control," the official said.

"It is legitimate and legal," she said, adding that differences between Russia and the United States regarding Moscow's nuclear cooperation with Iran were "narrowing."

Under the accord between Russia and Iran signed in February, Russia is to send nearly 100 tonnes of fuel to Iran in several consignments under IAEA supervision.