The commander of Basra’s police force said today that the massive bomb that killed four British soldiers yesterday morning was similar to Iranian-made devices that have been used to deadly effect in other parts of Iraq.

British army officials said their own explosives experts had completed their assessment of the device that destroyed the 24-tonne Warrior armoured personnel carrier, but refused to either confirm or deny the commander’s claim.

Major General Mohammed al-Moussawi said such a device had not been used in southern Iraq before. But he said two similar bombs had been discovered yesterday morning in Basra, one on the road leading to the British base at Basra Palace and another in the same western district of Hayaniyah where the Warrior armoured personal carrier was blown up in the early hours of yesterday.

Suspicion has fallen on a rogue faction of the Mahdi Army, the Shia militia nominally under command of the virulently anti-western cleric Hojetoleslam Moqtada al-Sadr. Hayaniyah is an area where the Mahdi Army holds sway.

Officials believe the anti-British operations to be the work of a Mahdi faction that has drifted away the main current of the nationalist Shia force and come under the influence of Iran. While Iranian influence on the militia as a whole is believed to be limited in scope, the small groups affiliated with Tehran receive disproportional amounts of funding and weaponry from their eastern neighbour.

Hojetoleslam al-Sadr himself is believed to be in Iran at present, keeping a low profile during an extensive US security crackdown on Baghdad, where his sprawling militia is accused of running death squads that have killed hundreds of Sunnis.

But British officials were sceptical that the police commander - a widely respected officer in Basra who is not affiliated to any of the main parties -- could have drawn so definite a conclusion so quickly on Iran’s alleged involvement in the attack.

“I’d be surprised if we were able to say where the components came from. People can surmise, but unless you see 'Made in Iran’ or see them carrying it across the border it is very difficult to say,” said Lieutenant Colonel Kevin Stratford-Wright.

He said details of the device would not be released to avoid giving anti-coalition force's “battle damage assessment”. But initial estimates had indicated that the lethal blast was not a so-called explosively formed projectile, or EFP, which generally explode from the side of the road.

The detonation that destroyed the Warrior exploded underneath the vehicle.

The US military has claimed in recent months that Iran is equipping Shia militias with EFPs, which fire a fist-sized disc of armour-piercing molten copper that explodes inside a military vehicle, and is triggered by an infra-red system that is extremely difficult to jam.

In the complex and often overlapping web of militias, tribes and criminal gangs that jostle for control of Basra, fingers were yesterday being pointed at all kinds of different parties.

“It’s a strong message from Iran to say, 'We can attack any British or American target in Iraq if you interfere in our affairs,’” said a professor of political science at Basra University who asked not to be identified.

But Kerim Refat, a computer analyst, insisted that the explosion was the work of anti-Iranian Sunni extremists trying to provoke hostility toward Iran. “It’s a clever manipulation of the situation. Sunni groups may be stoking feelings against Iran,” he said.

Lt Col Stratford-Wright declined to comment on which group might have been behind the attack, though most of the major British raids targeting “terrorists” in the south have netted Mahdi Army commanders. “You can bet you life we are looking for them,” he said.

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