The US military claimed yesterday that 170 soldiers had been killed in Iraq by sophisticated armour-piercing weapons supplied by Iranian agents acting on behalf of the highest levels of the Tehran Government.

Senior officials in Baghdad also claimed that five Iranians, arrested last month in a controversial raid in Irbil, were members of the Iranian Revolutionary Guard Corps. They said that the group, all carrying false papers, had been caught flushing documents down lavatories and shaving their heads to disguise their appearance. One allegedly had “explosive residue” on his hands.

The revelations were greeted with caution by journalists because of their timing, coinciding with Washington intensifying the pressure on Tehran over its nuclear programme.

The suspicion was heightened by officials refusing to be named and forbidding filming of the briefing, in which they put on display a cache of the weapons allegedly involved. However, British military and officials in Iraq believe that Iran is arming, training and financing Iraqi insurgents, mostly linked to Hojatoleslam Moqtada al-Sadr’s al-Mahdi Army.

In Baghdad the material displayed by the US-led coalition officials included one green 81mm mortar round, half a dozen 60mm rounds and two rocket-propelled grenades — all stamped 2006 in English. There were also fragments of tailfins and one of the armour-piercing “Explosively Formed Penetrators” (EFPs) that US officials allege Iran is supplying to its “proxies” among Iraq’s anticoalition Shia factions. Asked why the coalition chose to make the claims now — two years after the threat posed by EFPs was identified — one senior official said their use had “dramatically increased”.

“There is a growing body of evidence pointing to the Iranian supply of such EFPs to Iraqi extremist groups; additional evidence suggests that Iran is providing training and weapons to extremist groups in Iraq,” he said. An explosives expert claimed that the engineering of some components indicated that they had been manufactured outside Iraq. In particular, the EFPs’ design was, he said, uniquely Iranian: a thick plastic cylinder, packed with explosives. They explode when an infra-red system detects a vehicle, hurling out a “molten jet” of copper that punches through armour plating.

However, one analyst said that Tehran operated through proxies. “An Iranian standing over an American with a smoking gun is never going to happen. It’s plausible deniability.”

Further south, British forces say that while no direct involvement by Iranian operatives has been uncovered, three containers of explosives were seized near the Iranian border. “I can’t prove it came from Iran,” he said, “but we are a few miles from the border. How else did it get here?”

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