Taleban insurgents killed three British Nato soldiers in an ambush in Afghanistan’s southern province of Helmand today, just 24 hours after the alliance took over operations in the country’s lawless south.

It was the biggest loss of life sustained by British troops in Afghanistan in a single day since a coalition of Western forces, led by the United States, toppled the Taleban in 2001.

A total of 16 British soldiers have now been killed in Afghanistan - nine of them since the deployment in April of 4,000 British troops to Helmand, Afghanistan’s main opium producing region.

Another British soldier was killed in Iraq, the first to die from a mortar attack on one of the British bases in Basra.

Corporal Matthew Cornish, 29, a member of the 1st Battalion The Light Infantry, had served in Iraq on two other occasions, as well as in Sierra Leone and Northern Ireland. He was married with two children.

There have been frequent mortar attacks in the past but none has previously caused serious casualties. The total number of Britain’s troops who have died under enemy fire in the two campaigns now stands at 97.

Today's ambush in Afghanistan occurred around 7.30am local time as British forces launched a major assault against the Taleban involving land forces, Apache helicopters and Harrier jets, military officials said.

They were ambushed while engaged in a large-scale operation to relieve a group of several dozen paratroopers who had faced daily attacks over a sustained period.

However, at the start of the relief operation, two British Army vehicles, believed to be armoured Pinzgauer carriers, were targeted by the Taleban.

One, containing the three soldiers who died, was blown up and the other was severely damaged. The worst-hit vehicle was so badly wrecked that it took time to extract the bodies. A fourth soldier was seriously wounded and evacuated to a military hospital. His condition was described as critical.

British forces returned fire and killed several Taleban during a gunfight that lasted several hours, although casualties on their side had yet to be confirmed.

"This was part of a deliberate, planned operation against the Taleban, based on intelligence reports. We knew where the Taleban were," Brigadier Ed Butler, commander of British forces in Afghanistan, said.

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