"The Iranians have in their normal way just before the pressure really gets too much.. come with another offer," the diplomat said on condition of anonymity.

Western diplomats in Vienna earlier said Iran was ready to renounce its efforts to assemble centrifuges to enrich uranium and that an agreement with the leaders of Britain, France and Germany appeared imminent.

The report came less than a week before a key meeting of the board of governors of the UN nuclear watchdog, the International Atomic Energy Agency (IAEA) on September 13 to review Iran's nuclear program.

But the diplomat in London said that Tehran had skirted around the most sensitive issues.

"We are not close to a deal," he warned.

"They have told the IAEA board... that they were re-suspending some of their activities (but) they did not choose to suspend the key thing, which is uranium enrichment," he said.

"They didn't look at the uranium conversion facility. They are explicitly continuing with that and they just offered one or two other things which were pretty minor.

"It just looks like they are offering something so that when it comes to the board next week they are able to tell us that they have done something to try to meet us half-way," he added.

He also stressed that Tehran's proposal had been made to the IAEA, not to Britain, Germany and France, which have reportedly been negotiating for three days to persuade Iran to suspend all uranium enrichment activities.

A Foreign Office spokesman declined to comment, saying: "We will have to wait and see what this means in the IAEA board, which is meeting on Monday."

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