"I have promised to clear up the date when the construction of the Bushehr power plant will be completed but can say for sure that the station will not be launched before the end of 2008," RIA news agency quoted Sergei Shmatko, the president of state-run Atomstroiexport, as saying during a visit to China.
Russia said on December 17 it had delivered the first shipment of nuclear fuel to Bushehr, a step Moscow and Washington said should convince Tehran to shut down its own disputed uranium enrichment program.
Iran, however, said it would not halt its efforts to enrich uranium - fuel it says it needs for other power plants but which Western powers fear could be used in a nuclear bomb.
Shmatko told Russian reporters in Lianyungang that the timing for the completion of Bushehr had been agreed with Iran but it did not involve a specific date.
A clear date would be added later, he was quoted as saying by Interfax news agency.
Atomstroiexport is building the nuclear reactors at the Bushehr plant, with the fuel supplied from Rosatom, the Russian state atomic energy agency.
Russia says Bushehr is being built under the supervision of the United Nations' nuclear watchdog, ruling out any military use for the fuel or technology.