Sergei Kiriyenko said at a meeting with Prime Minister Vladimir Putin that the uranium fuel will be loaded into the reactor in Iran's southern port of Bushehr on Saturday.
"That marks the beginning of the physical startup of the plant and turns it from a site under construction to a functioning facility," he said in televised remarks.
Iranian officials have said it could take about a month before the plant starts providing electricity to the Iranian cities.
Kiriyenko told Putin that the startup is a "landmark event" that will show that Russia respects its international obligations.
"We have proven that Russia always fulfills its obligations," he said, adding that Russia has argued that every country, including Iran, has the right for peaceful use of nuclear energy if it accepts international controls and norms.
"I congratulate you on that," Putin said.
Russia has argued that the Bushehr project is essential for persuading Iran to cooperate with the UN nuclear watchdog and fulfill its obligations under international nuclear nonproliferation agreements.
Russia signed a $1 billion contract to build the plant in 1995, and supplied the uranium fuel for it more than two years ago, but the launch has been put off for years.
Delaying the project has given Russia continued influence with Iran in international attempts to have it stop uranium enrichment — a program Iran says it needs to make fuel for an envisaged reactor network but which also can be used to build atomic weapons.
The terms of the deal commit the Iranians to allow the Russians to retrieve all used reactor fuel for reprocessing to exclude a possibility of Iran using plutonium contained in the spent fuel to make nuclear weapons. Iran has said that International Atomic Energy Agency experts will be able to verify that none of the fresh fuel or waste is diverted.
Still, the US sees the Russian move to launch the Bushehr reactor as a false signal to Tehran as Washington strives to isolate Iran politically and economically to force it to compromise on enrichment.
Russia has walked a fine line on Iran for years. One of six world powers leading international efforts to ensure Iran does not develop a nuclear weapon, it has strongly criticized the US and the European Union for following up with separate sanctions after the latest UN penalties — which Moscow supported — were passed.
