"They have to start to fire it up mid-2006. The fuel has to be at the plant six months before that," Alexander Rumyantsev, the head of the Russian atomic agency said in an interview due for publication in daily Vremia Novosti, quoted by the Ria Novosti news agency.

Under the accord between Russia and Iran signed in February, Russia is to send nearly 100 tonnes of fuel in several consignments under the supervision of the International Atomic Energy Agency (IAEA).

"All the necessary precautions have been made in line with international standards," Rumyantsev said.

The United States alleges that the Bushehr nuclear power plant in southern Iran is part of a cover for weapons development.

Washington is convinced that Iran is seeking to build atomic weapons -- charges that Tehran denies -- and has been trying to convince Moscow to halt its nuclear cooperation.

As a concession to Western concerns, Russia will fuel the reactor on condition that Iran sends back spent fuel, which could potentially be upgraded to weapons use.

Tehran initially rejected the condition, but eventually relented after two years of negotiations.