Iran's first nuclear power station has begun loading fuel and will be declared operational in a ceremony attended by Iranian and Russian officials.
Nationwide celebrations are planned to mark the event at the Bushehr reactor in southern Iran, the BBC reports.
Russia will operate the plant, supplying its nuclear fuel and taking away the nuclear waste.
Iran has been subject to four rounds of United Nations sanctions because of its separate uranium enrichment programme. The West fears Tehran wants to build a nuclear weapon, but Iran insists its plans are for peaceful energy production.
The Bushehr facility, which has taken 35 years to build, has been plagued by delays.