The agencies quoted Russian nuclear agency chief Sergei Kiriyenko as saying builders are in the final stages of work on the plant near the city of Bushehr.
His remarks Saturday were in line with a statement by the head of the Russian company building the plant that it would not be started up before late 2008. But Iran has said the reactor would begin operating at half its capacity this summer.
Russia has been building Iran's first nuclear power plant for more than a decade. Delays have prompted speculation that Moscow has used the project to pressure Iran to halt nuclear activities.
Also on Saturday, Iran demanded action from the UN Security Council about an Israeli threat to attack its nuclear sites if it continues uranium enrichment, according to a letter released on Saturday by Iranian UN Ambassador Mohammad Khazaee.
Israeli Transport Minister Shaul Mofaz was quoted on Friday in an Israeli newspaper saying that an attack on Iran looks "unavoidable" given the apparent failure of sanctions to deny Tehran technology with bomb-making potential.
Reuters contributed to the report