Iran may be just a year away from having the capacity to build a nuclear bomb - if its claims that it has stepped up production of enriched uranium to an industrial scale are to be believed.

However, Western nuclear analysts reacted with a mixture of apprehension and scepticism to Tehran's announcement yesterday that it had begun operating nearly 3000 centrifuges - the devices used to enrich uranium for use in reactors and bombs.

Though the regime insists its boosted uranium enrichment capacity - nearly 10 times the previous level - would only be used to provide fuel for its nuclear power plants, this could produce enough of the substance for a nuclear bomb within a year.

But there were doubts over whether the centrifuges, which increase the proportion of the uranium 235 isotope in the material, would be able to run efficiently or consistently.

Previously Tehran has been quick to announce leaps forward in its nuclear programme whilst brushing over technological difficulties.

Most light-water nuclear reactors use uranium which is enriched to contain around 3% to 4% uranium 235. Weapons-grade uranium and that used in nuclear submarines has a much higher level of the isotope, typically over 85%.

Iran is known to have had 328 centrifuges operating at its Natanz facility in central Iran. For months, it has been saying it plans to launch an expanded programme of 3000 devices, likely to be set up in an underground area at Natanz to protect them from air strikes.

In a ceremony at Natanz marking the one-year anniversary of the first successful enrichment of uranium there, President Mahmoud Ahmadinejad said: "I declare that as of today our dear country has joined the nuclear club of nations and can produce nuclear fuel on an industrial scale."

Asked by reporters if Iran has begun injecting uranium gas into 3000 centrifuges for enrichment, Iran's top nuclear negotiator, Ali Larijani replied: "Yes." He did not elaborate if all were working.

Vice President Gholamreza Aghazadeh told Iranian state television that the installation of the 3000 centrifuges was not the end of the project.

"It's completely the reverse," he said. "This trend of installing machines will permanently continue until 50,000 centrifuges have been installed."

In the enrichment process, uranium gas is pumped into centrifuges, which spin and purify the gas.

Enriched to a low degree, the result is fuel for a reactor, but to a high degree it creates the material suitable for a nuclear warhead.

The US and its allies have accused Iran of seeking to develop weapons, a charge Tehran denies.

The announcement is in open defiance of the International Atomic Energy Authority and risks provoking greater sanctions from the United Nations.

But Michael Levi, a nonproliferation expert at the Washington-based Council on Foreign Relations, said it was more likely to reflect President's Ahmadinejad's desire to increase support at home and appear strong abroad than a realistic assessment of Iran's nuclear capacity.