Sergei Kiriyenko said earlier in the day that Russia had completed the construction of Iran's first nuclear power plant at Bushehr and would soon launch a trial run.
He did not say when the plant would go into operation, commenting that this would depend on the outcome of the testing.
"We're unable at this stage to set an exact date for the launch; we have an agreed-on testing and inspection schedule," he said. "The actual date will depend on how these tests proceed."
The plant in south Iran, which Russia undertook to finish as part of a 1998 contract, was originally scheduled to go on line at the end of 2006, but the date has been pushed back several times.
Kiriyenko previously said that under the Russian-Iranian contract, Russian experts would operate the plant's first reactor and create a team of skilled Russian staff.
Iranian Foreign Minister Manouchehr Mottaki said earlier the Bushehr plant would go on stream in the first half of 2009.
In December 2007-January 2008, Russia supplied nuclear fuel for the plant under control of the International Atomic Energy Agency (IAEA), the UN nuclear watchdog. Iran has agreed to return spent nuclear fuel to Russia.
The construction of the Bushehr plant was started in 1975 by German companies. However, the German firms stopped work after a U.S. embargo on hi-tech supplies to Iran was imposed following the 1979 Islamic Revolution and the subsequent seizure of the U.S. embassy in Tehran by radical students.