"The last word is after this period, which I do not assume will exceed six months ... we must seriously and firmly follow enrichment programmes and use the very important advantages of nuclear technology," he said.

"So far, we have reached the point that we accept to suspend parts of our activities for a period that was not necessary at all. Our negotiators have tried to shorten this period and we interpret it to be about two, three months up to six months," the prominent cleric said at Friday prayers.

Earlier this week the International Atomic Energy Agency (IAEA) spared Iran the fate of being referred to the UN Security Council for possible sanctions after Tehran agreed in a deal with Britain, France and Germany to suspend its uranium enrichment programme.

The United States accuses Iran of running a covert nuclear weapons programme, but the Islamic republic insists it only wants to enrich uranium to low levels, so as to produce fuel for a series of atomic power stations designed.