After decades of delay, engineers finally began loading the Russia-supplied fuel into the plant in the southern port of Bushehr, in the presence of International Atomic Energy Agency (IAEA) inspectors, a statement by Iran's Atomic Energy Organisation said.
“The operation of transferring nuclear fuel to the reactor was carried out on 30th of Mordad (August 21) in presence of Ali Akbar Salehi, vice president and head of Iran's atomic body, and Sergei Kiriyenko,” the head of Russian atomic body, Rosatom, the statement said.
It said the 163 rods of fuel will be “transferred into the core of the reactor after necessary inspections.”
Last week, Salehi said the transfer of fuel into the reactor would be complete by September 5.
On Friday, Iranian Atomic Energy Organisation spokesman Ali Shirzadian said the one-billion-dollar plant's actual commissioning would come in October or November when the electricity it generates connects to the national grid.
The much-anticipated launch comes despite the fact that Moscow, a long-time nuclear ally, has hardened its position on Tehran's nuclear programme.
In June, Russia backed a fourth round of UN sanctions against Iran over its uranium enrichment, the most controversial part of its atomic programme and which the West believes is aimed at making nuclear weapons, a charge Tehran strongly denies.
Iran says it is enriching uranium to power nuclear reactors so it can eventually generate electricity of around 20,000 megawatts.
Iran insists it needs nuclear power for when its fossil fuels eventually run out.
On Friday, Salehi said Iran will continue enriching uranium to make fuel for the Bushehr plant as Tehran might not always buy it from Moscow.
“The Bushehr plant has a lifespan of 60 years and we plan to use it for 40 years. Suppose we buy fuel for 10 years from Russia. What are we going to do for the next 30 to 50 years?” state news agency IRNA quoted him as saying.
Russia has already supplied 82 tonnes of fuel for Bushehr and plans to take back the spent material to avoid any misuse.
On Wednesday, Russian Foreign Minister Sergei Lavrov said the Bushehr plant would keep Iran firmly fixed to the peaceful use of nuclear power.
“It is a most important anchor which keeps Iran within the regime of non-proliferation,” he said.
Mark Fitzpatrick, an expert in non-proliferation at the International Institute for Strategic Studies in London, said Bushehr is not a proliferation risk “as long as it is run to produce power for electricity generation.”
“It would be a risk if Iran operated it differently, i.e. for short periods at low-burn up in order to produce weapons-usable plutonium — but in this case the IAEA would know,” he said of the UN atomic watchdog.
Work on the Bushehr plant, which is not targeted under UN or other sanctions, began in the 1970s under the rule of the US-backed shah using contractors from German firm Siemens.
The project was shelved when the shah was toppled in the 1979 Islamic revolution, and was revived a decade later under current supreme leader Ali Khamenei.
In 1994, Russia agreed to complete its construction, but since then “technical problems” and squabbling between Moscow and Tehran delayed its completion.
Fresh doubts over Bushehr were raised after Moscow voted for the latest UN sanctions, followed by Russian President Dmitry Medvedev commenting that Tehran was close to attaining the potential to build a nuclear weapon.
This triggered an angry response from Iran, as Moscow's position has always been that Tehran has the right to peaceful nuclear energy.
Ali Asghar Soltanieh, Iran's envoy to the IAEA, accused Moscow of delaying Bushehr's start-up, saying “it is hard to believe that the technical issues continue to delay the completion of the plant over the past 15 years.”
Bushehr has always been seen as a potential target in the event of a military strike by Iran's arch-foes the United States and Israel which have never ruled out military action against Tehran's nuclear programme.