Iran has said it is pressing ahead with its nuclear programme despite recent sanctions by the UN Security Council.
Iran insists its nuclear programme in peaceful
An official said Iran is moving towards the industrial production of nuclear fuel, with the installation of 3,000 centrifuges for enriching uranium.
President Mahmoud Ahmadinejad told Reuters Iran was planning to expand its facilities "very soon, bit by bit".
Iran insists its nuclear programme is peaceful and aimed at producing energy, denying US claims it is making a bomb.
Monday's statement came after diplomats in Vienna began to worry that there was so little activity at Iran's main nuclear site that perhaps work had started on a secret site elsewhere in the country.
UN SANCTIONS ON IRAN
Ban on import and export of nuclear-related material
Assets frozen of 10 companies and 12 individuals
Threat of further non-military sanctions
"We are moving towards production of nuclear fuel which needs 3,000 centrifuges and more... This plan is going ahead and is moving towards completion," Iranian government spokesman Gholamhossein Elham said.
"We need to produce fuel on an industrial scale for [our] power plants," he said.
Centrifuges are the machines than spin uranium gas to enrich it to low levels for fuel and much higher levels for nuclear weapons.
So far Iran has succeeded in connecting two cascades of 164 centrifuges each - a limited achievement considering thousands of machines are needed to produce enough fuel for a power plant, says the BBC's Frances Harrison in Tehran.
The Security Council passed a resolution on 23 December 2006 banning the supply of nuclear-related technology and materials to Iran and imposing an asset freeze on key individuals and companies.
Iranian officials have been defiant since, vowing to press ahead with plans to install 3,000 centrifuges.
Our correspondent says this is likely to be the nuclear achievement the country has promised to announce next month, to coincide with the anniversary of the revolution.
But what is not clear is whether Iran is just going to install the machines at its enrichment site or whether it is going to operate all 3,000 and run them successfully to produce fuel.