The operation to load fuel into Iran's first nuclear power station has begun amid nationwide celebration.
Russian engineers will operate the Bushehr plant in southern Iran, supplying its nuclear fuel and taking away the nuclear waste.
At the inauguration of the plant today, the head of the Iran's atomic energy organisation, Ali Akbar Salehi, said it demonstrated that the country's nuclear aims were entirely peaceful - an assertion that the US questions.
Describing the plant as a symbol of Iranian resistance, Salehi added: "Despite all pressure, sanctions and hardships imposed by western nations, we are now witnessing the start-up of the largest symbol of Iran's peaceful nuclear activities."
The first truckload of fuel was taken today from a storage site to a fuel pool inside the reactor building under the watch of monitors from the UN's International Atomic Energy Agency. Over the next two weeks, 163 fuel assemblies, equal to 80 tonnes of uranium fuel, will be moved inside the building and then into the reactor core.
It will be another two months before the 1,000-megawatt, light water reactor begins supplying electricity to Iranian cities.
Russia, which helped finish building the plant, has pledged to safeguard the site and prevent spent nuclear fuel from being used to make nuclear weapons. Moscow believes the Bushehr project is essential in persuading Iran to cooperate with international efforts to ensure it does not develop nuclear arms.
Washington disagrees, arguing that Iran should not be rewarded while it continues to defy UN demands to halt the enrichment of uranium, a process used to produce fuel for power plants but which can also be used in weapons production.
The Bushehr plant poses little proliferation risk since Russia is supplying the enriched uranium for the reactor and will take away spent fuel that could be used to make weapons-grade plutonium.
President Mahmoud Ahmadinejad said yesterday that Iran would stop enriching uranium to a high grade if it was assured of the supplies it needed for a research reactor.