The head of Russia's state nuclear power corporation Rosatom Sergei Kiriyenko announced earlier on Wednesday that Russia had completed the construction of Iran's first nuclear power plant at Bushehr and was launching start-up operations.
"Iranians are showing again that they are making progress in their nuclear race," Foreign Ministry spokesman Yigal Palmor said. "This should be understood as very bad news for the whole of the international community."
Palmor called for "immediate and very determined steps" to prevent Iran from becoming a nuclear power.
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.
Foreign Minister Manouchehr Mottaki has said it will go on stream in the first half of 2009. A Russian deputy foreign minister said last Friday the plant would be commissioned according to the schedule agreed on with Tehran.
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.