Under the deal Iran would freeze all nuclear fuel enrichment and reprocessing activities until it has reached a final agreement with the EU over a package of economic, technological and security incentives in return for abandoning potentially weapons-related nuclear activities, the diplomats said.

"The time frame (of the enrichment suspension) will be given by the pace of reaching overall agreement," an EU diplomat said.

A deal with the EU trio of Britain, Germany and France is Iran's best hope of avoiding a showdown with the United States in the U.N. Security Council.

Recently re-elected U.S. President George W. Bush has dubbed Iran an "axis of evil" member and vowed to prevent it from acquiring nuclear arms. Israel also refuses to rule out strategic strikes against Iran's nuclear facilities.

Washington wants Iran's case sent to the Security Council but agreed last month to give the EU trio a final opportunity to negotiate a solution with Iran, which says its nuclear plants will only be used for a civilian atomic energy programme.

The EU trio told Iran it must freeze uranium enrichment - a process used to purify uranium into nuclear reactor fuel or to make bomb-grade material - before the Nov. 25 board meeting of the U.N.'s atomic watchdog or face the Security Council.

"Negotiations were very hard and complicated but we reached a preliminary agreement on an expertise level," said Hossein Mousavian, head of Iran's delegation in Paris. "It is a framework that contains the viewpoints of all sides."

Iranian Foreign Minister Kamal Kharrazi said: "The talks realised big progress and we need to reach a final agreement."

"The important thing is that there was acknowledgement that Iran is a country with a peaceful nuclear technology," he said in comments aired by Arab television.

NO TIME LIMIT ON SUSPENSION "All four delegations are supposed to go to their capitals and if the capitals agree with the agreement, it will be officially announced in the next few days," Mousavian said.

He told Iranian television Iran had agreed to a voluntary suspension of enrichment whose duration would be set by Tehran, which earlier said the suspension could be six months at most.

But EU diplomats said the wording would be fudged so that no precise time limit is placed on the suspension. Instead it would last until negotiations conclude on a follow-up deal over a package of EU incentives including help with a peaceful nuclear energy programme and the resumption of stalled trade talks.

To receive those incentives Iran would have to agree to scrap its nuclear fuel cycle activities for good - something it has repeatedly said it will never do.

Publicly EU officials would only say that the two sides were edging closer to a deal.

"The talks concluded with considerable progress," said Cristina Gallach, spokeswoman for EU Foreign Policy chief Javier Solana. "They came close to a provisional agreement."

Some non-EU diplomats expressed concern that Iran would use a deal with the EU to ease international pressure only to resume uranium enrichment activities further down the line.

A previous agreement between the EU trio and Iran signed in October 2003 unravelled this summer when Iran pulled out of a pledge to stop making and assembling enrichment centrifuges and announced plans to process tonnes of raw uranium.

(Additional reporting by Paul Taylor and Gilles Castonguay in Brussels, and Dubai newsroom)