Updated

Russia and Iran delayed signing a deal Saturday that would deliver nuclear fuel to the Middle East country for the startup of its first reactor — a project the United States has pushed Moscow to drop, claiming Iran (search) is trying to build a nuclear bomb.

Top Russian and Iranian nuclear officials said the signing of the agreement was expected to occur Sunday in Bushehr (search), the southern town where Iran's first nuclear power reactor was built using Russian help.

The last-minute snags followed Thursday's summit between President Bush and Russian President Vladimir Putin (search) in Slovakia, which touched on American concerns over Russian support for Iran's contentious nuclear program.

Putin has said he is sure Iran does not intend to build nuclear weapons and that Russian cooperation with Tehran would continue.

Under the deal, Russia will provide nuclear fuel to Iran, then take back the spent fuel, a step meant as a safeguard to ensure it cannot be diverted into a weapons program. Iran has also agreed to allow the U.N. nuclear watchdog agency, the International Atomic Energy Agency, to monitor Bushehr and the fuel deliveries.

Russia helped build the $800 million reactor at Bushehr, whose construction is now complete. Operations are set to begin in late 2005 or early 2006 at the light-water reactor, which is capable of generating 1,000 megawatts of electricity. Experts say spent fuel from the Bushehr reactor could be used to produce enough plutonium to make 30 rudimentary atomic bombs a year.

Mohammad Saeedi, deputy head of Iran's Atomic Energy Organization, attributed Saturday's postponement to differences over the delivery time of the first shipment of fuel and the launch of the Bushehr plant.

But he said the deal will be signed.

"Remaining issues are to be resolved tonight and the agreement is to be signed in Bushehr Sunday," he said.

Saeedi said Iran wanted the fuel shipment to arrive at least two months sooner than the Russians suggested.

The head of Russia's Federal Atomic Energy Agency, Alexander Rumyantsev played down concerns over the postponement, saying both sides likely will seal the deal Sunday. Rumyantsev is in Iran to participate in the signing.

Washington has pressed Moscow to call off the deal, saying Iran could use the Bushehr reactor as part of a nuclear-weapons program. Iran rejects claims it wants to build nuclear weapons, saying it is pursuing a peaceful nuclear program to produce energy.

The Bushehr deal comes as Europe is trying to persuade Iran to rein in its nuclear program.

Britain, France and Germany are trying to secure an Iranian commitment to scrap enrichment plans in exchange for economic aid, technical support and backing for Tehran's efforts to join mainstream international organizations. Iran has suspended enrichment-related activities during talks with the Europeans but insists the freeze will be brief.

Also Saturday, diplomats familiar with the IAEA's work said Iran used its links to the black market to accumulate the knowledge it needed by the late 1980s to set up technology that can be used to make nuclear weapons.

An agency investigation during the past two years established that Iran ran a clandestine nuclear program for nearly 20 years, including working on uranium enrichment — which can be used to make weapons.