Furthermore, Iran's nuclear programme is at a relatively embryonic stage and does not pose any immediate threat to world security, they said.

"The key thing is they are being more open. They seem to have taken on board the message that, in the current international climate, you cannot go around hiding these things," said one Tehran-based European diplomat.

That message was conveyed to Iranian officials in no uncertain terms during the visits of Iranian Foreign Minister Kamal Kharrazi to London and European Union Commissioner Chris Patten to Tehran earlier this month, diplomats said.

The diplomatic pressure, combined with the impending visit of International Atomic Energy Agency head Mohamed ElBaradei to Tehran later this month, explained the timing of Iran's declarations about its nuclear ambitions, diplomats said.

IAEA VISIT KEY TO TIMING

"ElBaradei's visit is the key to the timing of this announcement. The Iranians seem to be well aware that they must cooperate with the IAEA or risk coming under the spotlight," an Asian diplomat said.

"As long as they keep cooperating, the chances that they could turn this to sinister purposes remain relatively remote," the European diplomat said.

Iran, which is a signatory of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT), insists its nuclear plans are entirely peaceful.

President Mohammad Khatami, in a forthright speech on Sunday, said Iran had begun mining uranium and was constructing facilities that would enable it to manage the entire fuel cycle, including managing spent fuel, within the country.

The IAEA took the announcement in its stride, suggesting it was aware of Iran's plans. ElBaradei is due to visit Iran later this month to verify Tehran's claims.

US officials argue that Iran, with abundant oil and gas reserves, has no need to develop a costly atomic power industry.

They also say it does not need such a range of nuclear facilities, given an existing agreement between Tehran and Moscow for Russia to provide the uranium and manage spent fuel from Iran's first nuclear reactor in the southwestern port of Bushehr.

But Iranian officials say the 1,000 MW Bushehr plant, due to come on stream by early 2004, is insufficient to meet booming electricity demand from the country's 65 million people.

They say they need to be generating 6,000 MW from nuclear power in 20 years time and to do that means ensuring an independent uranium fuel supply.

KHATAMI WANTS SELF-RELIANCE

"We cannot rely on others who could become influenced by different elements," Khatami said, in an apparent reference to US pressure on Moscow to stop helping Iran with its nuclear programme.

A uranium processing plant is close to completion in the central city Isfahan and preliminary work has begun on a uranium enrichment facility.

Uranium must be enriched before it can be used in nuclear reactors to generate electricity. But highly enriched uranium is also a key ingredient for nuclear weapons.

Diplomats said the details announced this week were the first public admission of what Western governments had known for some time. "It's not new news, but it was public news," said a Western diplomat in Tehran.

Gary Samore, a non-proliferation expert at London's International Institute for Strategic Studies, said Iran was probably two years away from producing the fissile material needed for nuclear weapons.

Even when the enrichment plant is completed, it will remain under close IAEA supervision, provided that Iran does not follow North Korea's example by pulling out of the NPT.

"It would be very difficult for Iran to use the facility to produce weapons-grade uranium without being caught," Samore said.