How close is Iran to a nuclear bomb?

In the coming days, Iran is expected to make what is being billed as a major announcement on its nuclear programme to coincide with the anniversary of the Iranian revolution.

But just how close is Iran to mastering nuclear technology?

Both Iran and some of its critics may have their own reasons for exaggerating the progress - but the real truth is hard to establish.

In its announcement, Iran may claim to have begun large-scale industrial enrichment of uranium.
But any statement is likely to be as much about political positioning as real technical progress, according to nuclear analysts.

The announcement may focus on work Iran has conducted in installing two cascades of more than 300 centrifuges in an underground industrial size plant at Natanz with the aim of moving towards a total of 3,000 machines.

The centrifuges are used to enrich uranium. This is in addition to two existing cascades in a pilot plant above ground.

But Iran's plan to initially run 3,000 centrifuges before moving towards an ultimate goal of 54,000 has run into obstacles and delays and is well behind target. Even the cascades in the pilot plant have seen problems.

However, once Iran has mastered the technology of enrichment and the ability to enrich gas at high speeds in a centrifuge then transferring it to a larger scale presents a lesser challenge.

Over the years, some of the problems with the programme seem to be due to Iran's own mistakes

For instance, one of the top figures in the programme has talked of how in the early days, those assembling the centrifuges did not wear cloth gloves.

As a result, tiny beads of sweat would be transferred to the rotor which spins inside the centrifuge.

This almost imperceptibly increased the weight of the rotor which then unbalanced the centrifuge when it started to spin, causing it to "explode".

Iran also was thought to have had problems with the purity of the uranium hexafluoride which is fed into the centrifuges, although its scientists now say this has been solved.

Over a number of years, both US and Israeli intelligence are believed to have covertly passed flawed parts and equipment to Iran to cause technical difficulties and slow the Iranian programme down.

It is possible that some of the electrical parts for Iran may have come through the Turkish end of the network run by Pakistani scientist AQ Khan which also supplied electrical components to the Libyan nuclear programme.

By the end of the network's activity in early 2004, it had been penetrated by British and American intelligence with some of the suppliers turned as agents.