The Iranian delegation in Russia was led by Mohammed Saeedi, vice president for international affairs at the Atomic Energy Organization of Iran.

"Today's meeting is to discuss the lack of funding of the project by the Iranian side," Pavlov, who heads the the plant's construction, said.

The Iranian delegation's visit follows Moscow's warning last month that payment delays would push back both Bushehr's planned September launch and the uranium fuel deliveries that had earlier been scheduled to begin this month.

Iran has been eager to get the uranium fuel, but Russian officials said it would only be delivered six months before the plant's launch.

Pavlov said that Russia was continuing construction work under the $1 billion Bushehr contract, but added that the talks would focus on "the impact of insufficient funding on the schedule of putting the reactor in operation".

Russian officials said last month that Iran was to pay Russia $25 million a month for construction work at the Bushehr plant but had paid only a fraction of the amount in recent months.

Yevgeniya Neimerovets, vice president of Atomstroiexport, said that Iran has not made any payments since January 17.

"The lack of payments has put our partners and subcontractors in a very difficult position," she said in a statement.

A tougher line?

Iranian officials have rejected the Russian claims that Tehran has failed to meet the payment schedule and suggested Moscow was caving in to international pressure to take a tougher line on Iran.

The funding dispute comes with persistent diplomatic efforts to persuade Iran to halt uranium enrichment in order to allay international fears that it could be seeking to build nuclear weapons.

In December, Russia supported a UN Security Council resolution imposing limited sanctions against Iran over its refusal to stop uranium enrichment, but the support came only after an initial proposal that would have imposed curbs on the Bushehr plant was dropped.

Russia emphasizes that Iran has the right to a peaceful nuclear energy program, and president Vladimir Putin and other officials repeatedly have said Moscow would honour the Bushehr contract.

The United States and some allies claim Iran's nuclear program is aimed at developing nuclear weapons, while Tehran maintains it is only intended to generate electricity.