Iran has begun loading fuel into its first nuclear power station in a ceremony attended by Russian officials.
Russia will operate the Bushehr plant in southern Iran, supplying its nuclear fuel and taking away the nuclear waste.
Iran has been subject to four rounds of UN sanctions because of its separate uranium enrichment programme.
Experts say that as long as the plant is Russian-operated, there is little immediate threat of its fuel being diverted to make bombs.
From Washington, the US state department said that it saw no "proliferation risk" from the plant. The UK also said had "always respected" Iran's right to civilian nuclear power.