Iran's Bushehr nuclear power station will not be operational until late 2008 at the earliest, the state-run Russian contractor building the site has said.
The US has backed Russian fuel deliveries to Bushehr
The announcement came days after Iran received its first delivery of enriched uranium from the company.
Russian officials have said previously that the plant could be working within six months of deliveries starting.
Tehran says it will not stop its domestic enrichment programme despite the threat of more UN sanctions.
BUSHEHR NUCLEAR PLANT
Begun in 1974 with German assistance
Work halts after Iran's 1979 Islamic revolution
Resumed in 1992 with Russian help
13 Dec: Russia and Iran agree to finish plant after numerous delays
Two pressurised water reactors
First to be completed in a year at the earliest
It insists it is pursuing peaceful power generation only, despite fears it could try to build a bomb.
Washington says Iran has no need to continue its own enrichment programme now that deliveries have started.
It says it supports the supply of enriched uranium to Iran as long as Moscow retrieves the fuel.
The head of Russian contractor Atomstroiexport, Sergei Shmatko, promised to give an exact date for the Bushehr site coming on stream later on.
The final delivery is due to be made in February, the company says.
Enriched uranium is used as fuel in nuclear power stations. When it is more highly enriched, it can be used to make nuclear weapons.