IRANIAN companies are obtaining prohibited American technology for use in roadside bombs that have killed more than 1,500 British and American troops in Iraq and Afghanistan.

Investigators say Dubai is being used as a gateway by Iran to acquire American-made components for use in a new generation of advanced roadside bombs - the biggest killer of troops in Iraq. More than 20 companies and individuals have been identified as trading in the components, which are banned for export to Iran.

Roadside bombs - known as improvised explosive devices (IEDs) - can pierce heavy armour and have proved to be the most effective and devastating weapons deployed by the insurgents. According to military commanders, the once rudimentary bombs now often use sophisticated electronics and infrared triggers to evade military countermeasures.

American companies legitimately export electronic components to the United Arab Emirates (UAE) and other countries, but it is alleged that these are then exported to Iran in breach of American sanctions.

A Georgia-based company was fined last month for supplying electronic circuit boards to Mayrow General Trading, based in Dubai, although it was unaware that its products might be destined for use in IEDs.

“We have reason to believe that Mayrow General Trading and its affiliates have been acquiring US-made components for use in improvised explosive devices in Iraq and Afghanistan,” said Mario Mancuso, the American undersecretary of commerce for industry and security. “We will do everything in our power to protect our forces in the field by prosecuting those who illegally export sensitive US technology.”

The American government says it has “specific and articulable” proof that the components are being used in IEDs. It has established that some of these products are being bought by Iranian front companies based in Dubai.

The Middle Eastern firms involved are not breaking any laws, but the UAE has in the past two weeks announced stricter controls on shipments which might violate national security.

A report commissioned by an international investigation company says the American sanctions - first imposed in 1979 - are routinely breached by Iranian front companies operating in the UAE. “These companies have [products] shipped to UAE and redirect the goods to Iran via air or sea,” says the report.

“In many cases the goods do not even leave the airport or port and get redirected immediately to Iran with no customs clearance in Dubai.”

One of the investigators said he had tracked US components which had been exported to a reputable distributor in Dubai. They were then bought by an Iranian front company, also in Dubai, and shipped to Tehran. The investigator identified the products on sale by their serial number.

About 1,500 servicemen - including more than 40 British troops - have been killed by IEDs since July 2003. The Pentagon is spending more than £3 billion developing countermeasures, but the devices are claiming a rising proportion of casualties.

Military commanders have repeatedly accused Iran of supplying the expertise and technology. Some of the bombs are said to be made in dedicated factories with specialised componentry.

Although no direct evidence has emerged of the involvement of the Iranian government in the construction of IEDs, a British commander said last week that coalition forces were effectively in conflict with Iran. Lieutenant-Colonel Patrick Sanders, commander of the 4 Rifles Battlegroup, said: “We are engaged, or we have been engaged, in a proxy war with Iran.”

The British Army accuses Iran of training and arming the Shi’ite militias in Iraq.

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