Energy Minister Sergei Shmatko stressed that politics had nothing to do with the decision, although the United States is seeking Moscow's help in pushing Tehran to allay Western fears about its nuclear program.
"The launch will not happen by the end of the year," Shmatko told reporters when asked if the station in southwest Iran would start up by the end of 2009, as previously scheduled.
"The engineers have to reach their findings," he said. "The building of the Bushehr station is defined absolutely 100 percent by technological conditions."
Russia's nuclear chief Sergei Kiriyenko, who heads the state holding company which controls the builder of the plant, said in February that the Bushehr launch was scheduled for 2009.
Moscow agreed to build the station in 1995 on the site of a plant begun in the 1970s by German firm Siemens. This project was disrupted by Iran's 1979 Islamic revolution and the 1980-88 Iran-Iraq war.
Diplomats say Russia uses Bushehr — and major arms contracts — as a lever in relations with Tehran, which is suspected by the United States and other Western powers of seeking to build a nuclear weapon.
Iran, the world's fourth-largest crude oil producer, rejects allegations that it is seeking to build an atomic bomb and says its nuclear program is aimed at generating electricity.
IRAN'S NUCLEAR PROGRAMME
Russian President Dmitry Medvedev said on Sunday after meeting U.S. leader Barack Obama in Singapore that Moscow was not completely happy about the pace of dialogue between Iran and the international community over Tehran's nuclear program.
Obama said time was running out for diplomacy after Iran failed to give a clear answer on a U.N.-drafted proposal to send low-enriched uranium to Russia and France, where it would be turned into fuel for a Tehran medical research reactor.
Russia started deliveries of nuclear fuel for Bushehr in late 2007, a step both Washington and Moscow said removed any need for Iran to have its own uranium enrichment program.
The contract to build the plant is a state secret, though it is estimated to be worth about $1 billion.
Russia says the plant is purely civilian and cannot be used for any weapons program as it will come under International Atomic Energy Agency supervision. Iran will have to return all spent fuel rods to Russia.
(Writing by Guy Faulconbridge, editing by David Stamp)
