"The Iranians are party to the non-proliferation agreement and no one is forbidding them to develop their own nuclear fuel cycle" which includes the process of enriching uranium for use as nuclear fuel, Alexander Rumyantsev, head of the Russian atomic energy agency, told reporters.

"But we are advising them not to do it and are demonstrating to them that it is economically disadvantageous," said Rumyantsev, the official who signed a landmark agreement in Iran on Sunday under which the Islamic state agreed to return spent nuclear fuel from a civilian power station.

"There are proven scientific documents which use mathematical calculations to show that for a country with fewer than eight or 10 nuclear reactor blocs, each capable of generating 1,000 megawatts, development of its own nuclear cycle is not just useless but ruinous," Rumyantsev said.

"We have explained this to the Iranians and they are closely studying these documents," he added.

Iran has said it is aiming to generate 7,000 megawatts of power through civilian nuclear reactors by the year 2020, substantially lower than the threshold cited by Rumyantsev for making the uranium enrichment process affordable.

Many countries are concerned that Iran could use a civilian nuclear power program as cover for clandestine efforts to develop the capacity to build nuclear weapons, an effort which would require capacity for enriching uranium to weapons-grade level.

Under the deal signed Sunday at Bushehr, the site in Iran of the country's first civilian nuclear power station which is still under construction, Iran agreed to return immediately to Russia all nuclear fuel after it has been spent in civilian reactors.

Germany, Britain and France -- the "EU-3" -- are pursuing efforts to persuade Iran through diplomatic pressure to drop any uranium enrichment ambitions. The United States has taken a tougher line, refusing to rule out military strikes against suspected nuclear weapons development facilities.

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