"The first casing with fuel is to be installed at the reactor in mid-2006," Alexander Rumyantsev, head of Russia's Atomic Energy Agency, was quoted as saying by RIA Novosti news agency.

"The fuel is supposed to arrive at the station half a year before that, although it is acceptable to send it three to four months in advance," RIA quoted him as telling Vremya Novostei newspaper in an interview to be published on Thursday.

The shipments schedule, closely watched by the United States and other Western powers, has been surrounded by secrecy. Officials have given little indication of the timing and Russian media have issued widely varying reports.

Iran, whose nuclear programme has raised deep suspicions in the United States and Israel, is under international pressure to do more to prove its activities are entirely peaceful.

Tension intensified this week when Tehran confirmed it would soon resume some sensitive nuclear work and end a freeze it agreed with the European Union in November.

Russia and Iran, whose nuclear ties date back to the early 1990s, have maintained the project is peaceful. But Moscow sounded tougher with Iran last month, saying it should do more to soothe international concerns.

Rumyantsev said Russia would supply 100 tonnes of nuclear fuel -- currently stored in Siberia -- to Iran by air and under strict surveillance by the UN nuclear watchdog, the IAEA.

After years of use, Iran will return all spent nuclear fuel to Russia, according to their agreement.

Once operational, Bushehr will generate 1,000 megawatts of electricity. Initiated before Iran's 1979 Islamic revolution and badly damaged during the 1980-88 Iran-Iraq war, the project was later revived with Russian help and has cost about $1 billion.