Officials from Iran and Russia, which has been involving in building the power station for the past 14 years, watched over the start of the pre-commissioning in the Gulf port of Bushehr.

"As for a timetable, the tests should take between four and six, seven months," the head of Iran's Atomic Energy Organisation Gholam Reza Aghazdeh said at a press conference in Bushehr.

"And if they go smoothly, then it (the launch of Bushehr) will be even sooner."

Tehran's ambitious nuclear drive has triggered a row with Western governments which suspect it is seeking to covertly build atomic weapons, a charge Iran strongly denies.

The visiting head of the Russian nuclear agency, Sergei Kiriyenko, announced that construction of the 1,000-megawatt plant had been completed but that Russia would remain involved for one year after it goes on stream.

"We have reached a deal to establish a joint venture to operate the plant," he said, adding that the two sides were also in talks to sign a 10-year contract for the delivery of fuel by Russia.

Despite being the world's number four crude oil producer and having the second largest gas reserves, Iran insists it needs nuclear power to sustain a growing population whose fossil fuels will run out in the next decades.

It has rejected repeated calls by the UN Security Council -- of which Russia is a permanent member -- for a halt to uranium enrichment, despite three sets of sanctions being imposed for its defiance.

Enrichment is the process that makes nuclear fuel for power plants but can also be diverted to make the fissile core of an atomic bomb.

The plant's start-up will be a leap forward in Iran's efforts to develop nuclear technology but is likely to further unnerve Western powers, rattled by the launch this month of an Iranian satellite on a home-built rocket.

Russia took over construction at Bushehr in 1995 but completion of the plant was delayed for a number of reasons, in particular the nuclear standoff between and Iran and the international community.

As part of the pre-launch process, Iran was carrying out comprehensive tests of equipment at the plant which Kiriyenko said involved loading dummy fuel rods into the reactor.

"Most of the systems have had more than 97 percent of the equipment installed," Kiriyenko said, saying some parts that required further testing included heat insulators.

"Other remaining equipment which should have been provided by third country could not be supplied because it broke the contract," he charged, but said the delay would not hinder the overall timetable.

Bushehr was first launched by the US-backed shah in the 1970s using contractors from German company Siemens but was shelved after the Islamic revolution until Russia became involved.

The UN nuclear watchdog, the International Atomic Energy Agency, said last week it had been informed by Tehran that the loading of fuel into the reactor was scheduled to take place during the second quarter of 2009.

The 87 tons of fuel supplied by Moscow is currently under IAEA seal.

All the main equipment at Bushehr has been installed by Russian contractor Atomstroiexport.

The IAEA, which has been investigating Iran's nuclear activities for six years, said in a report issued last Thursday that Tehran is continuing to enrich uranium, but has slowed down the expansion of its enrichment activities.

In all, IAEA inspectors had been able to verify that Iran has accumulated 839 kilogrammes (1,846 pounds) of low-enriched uranium, while Iran had told the agency that it had added another 171 kilogrammes this month.

Estimates vary, but analysts calculate that anywhere between 1,000-1,700 kilogrammes would be needed to convert into high-enriched uranium suitable for one bomb.

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