Russia's nuclear agency on Monday blamed internal wear-and-tear for the decision to remove fuel from the reactor of a nuclear power-plant it is building in Iran months before it was due to launch.

Iran had said Saturday it would remove fuel rods from the reactor of its Bushehr power plant on Russia's recommendation, in a setback for its controversial nuclear programme.

Rosatom said in a statement that it had discovered internal damage in one of the pumps of the coolant system, blaming Iran's insistence that the long-delayed project incorporate outdated equipment dating back to the 1970s.

It needs to check whether the fault caused tiny metal shavings to reach the reactor's fuel assembly via the water, the agency said.

"If we find metal shavings on the fuel assembly, all the assembly will be washed, the core of the reactor vessel cleaned, after which the fuel will be reloaded into the reactor of the power unit," it said.

The pumps "were part of equipment, supplied to the Bushehr site in the 1970s, which according to the contract, Russia was obliged to integrate into the project," it said.

It called the fault a "regular situation," that did not require bringing in more specialists or equipment.

Iranian officials have stressed that the glitch was not caused by the Stuxnet computer virus that targeted the country's nuclear programme in November.

The West suspects Iran's nuclear programme is a cover for a weapons drive -- a charge vehemently denied by Tehran -- but does not see Bushehr as posing any proliferation risk.

Iran had started loading the fuel into the reactor in October after the "physical launch" of the plant by Moscow on August 21 and the plant was set to begin generating electricity in April.

The project was first launched more than three decades ago, while Russia signed a deal with Iran in 1995 to complete the plant.

Bushehr is a pressurised water reactor with a capacity to produce 1,000 megawatts of power.

Iran, which has some of the world's largest oil and gas reserves, says it wants to develop nuclear power so it can use those reserves judiciously.