Russia and Iran have signed a deal in Moscow to launch Iran's nuclear reactor at Bushehr in September next year, officials in Moscow say.
Iran has missed a deadline to halt uranium enrichment
They say the Russian-built reactor will be fully operational in November 2007.
Iran had feared Russia would delay the launch because of international tension over Iran's nuclear activities, correspondents say.
The UN Security Council has told Iran to halt uranium enrichment amid fears it is trying to build nuclear arms.
Russian atomic energy agency spokesman Sergey Novikov said the date was fixed in an additional agreement to the original contract to build the reactor.
It came after Iranian officials apparently urged their Russian counterparts to speed up work to finish the plant.
Russian Security Council Chairman Igor Ivanov, quoted by Itar-Tass news agency, said Moscow would stand by its commitments.
After a meeting with visiting Iranian Vice-President Gholamreza Agazadeh, Mr Ivanov said the nuclear crisis could be solved by negotiation.
A compromise could be found which would recognise Tehran's right to develop nuclear energy for peaceful purposes, but which also addressed the concerns of the international community, he said.
The US wants UN sanctions against Iran over its failure to meet a 31 August deadline to stop enriching uranium.
Western powers accuse Iran of trying covertly to develop a nuclear bomb.
Iran maintains it has a right to a nuclear programme which, it says, is purely for civilian purposes.