Even as the ink was drying on the agreement signed by Russian and Iranian nuclear officials at the site of the Islamic republic's first nuclear power station, officials in Moscow tempered their satisfaction at the deal with fresh assurances that the process was under the tightest control.

"Russia's signature with Iran of the agreement on return of spent nuclear fuel does not mean that delivery of Russian nuclear fuel to this country is to start immediately," foreign ministry spokesman Alexander Yakovenko was quoted by Interfax news agency as saying.

The comment suggested that despite securing a legal go-ahead to proceed with its construction of the plant at Bushehr and winning the crucial commitment from Iran that many states have made a prerequisite for the plant to be built, Russia was nonetheless proceeding with high caution.

While the international consensus prior to Sunday's agreement suggested that a commitment from Iran to relinquish possession of spent nuclear fuel would be sufficient to assent to Russia's building of the plant, it was uncertain whether that view would hold as the project advanced.

The United States and Israel have led the charge against Iran's nuclear program, and on a swing through Europe earlier this month US Secretary of State Condoleezza Rice said Tehran's nuclear ambition "has to be seen in context as Iran is in other ways out of step" in the Middle East.

In Washington's tough line on Iran's nuclear program, many in Russia see not just an obvious concern to prevent the spread of weapons of mass destruction and try to enhance stability in the Middle East but also an unstated design to thwart Russia's commercial and strategic interests.

"The US is not using this subject as a strategic resource but as a bargaining chip in its relations with Russia," Konstantin Kosachyov, head of the Russian State Duma's foreign affairs committee, was quoted by Interfax news agency as saying earlier this month.

"The US's firm position on Iran is being used to drive back and limit Russia's positions," he said.

Those positions, from Moscow's point of view, include not just completion of the 800 million-dollar Bushehr nuclear power station but strategic commercialization of its civilian nuclear expertise at other projects in Iran, the Middle East and elsewhere in the world.

Several days prior to his summit meeting with US President George W. Bush in Bratislava last Thursday, President Vladimir Putin met at the Kremlin with Iran's top nuclear negotiator and said afterwards Russia was certain Iran had "no intention" of trying to manufacture a nuclear weapon.

Putin and Bush then sang in unison at the summit, with both leaders agreeing that Iran must not be permitted to acquire a nuclear weapon. Putin and other top Russian officials have stressed that few countries have more interest than Russia in making sure Iran does not get the bomb.

But behind the scenes in Washington, US officials and security experts question whether even the strictest verification measures would suffice to make certain Iran never acquired the capacity to enrich uranium to weapons-grade levels.

With US worries in mind, Russia has stressed that its contract for construction of a nuclear power plant in Iran violates no law or international agreement and will go ahead only if Tehran gives the watertight assurances the world has demanded that it will not pursue uranium enrichment.

"The Americans are against it," Viktor Kremenyuk, head of the Moscow-based think tank USA-Canada Institute, said of the Russian deal to build the plant in Iran.

"But we have told them: 'If you fear that this nuclear program could be used for military purposes, have the IAEA verify it'. Russia however will not accept... pressure from Washington to limit its own nuclear program."

Rose Gottemoeller, a former US official working on nuclear nonproliferation issues, wrote in an analysis published by the Carnegie Moscow Center that despite US concerns over the Russian project at Bushehr, Moscow may be better placed than anyone to contain Iran's nuclear program.

"In Iran, Russia's long-running diplomacy might enable progress toward goals that the United States could never achieve on its own, given the 25-year hiatus in direct contacts between Tehran and Washington," Gottemoeller, deputy undersecretary of energy for defense nuclear nonproliferation in the administration of former US president Bill Clinton, wrote.

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