The incident brings the total of UK military personnel killed in Afghanistan to 346.

A British soldier who died in southern Afghanistan yesterday was killed by cannon fire from a low-flying US aircraft, it emerged today.

The plane - believed to be an F18 - was on a "strafing run" after it was called in by British troops engaged in a gunfight with insurgents, according to defence officials.

The soldier, from 3rd Battalion the Parachute Regiment, died while on patrol in the Nad-e-Ali district of Helmand province. His relatives have been informed.

The Ministry of Defence said the incident would be the subject of a full investigation and that it would be inappropriate to comment further at this stage.

A spokesman for Isaf, the international force in Afghanistan, said: "While conducting a dismounted patrol, Afghan and coalition forces were engaged with enemy forces and requested close air support to suppress the enemy fire."

The soldier was part of an operation working to increase security in the district, the Task Force Helmand spokesman, Lieutenant Colonel David Eastman, said.

He added: "He has made the ultimate sacrifice protecting the people of Nad-e-Ali from insurgent intimidation and defending his country from the threat of terrorism. No more could be asked of any soldier. He will be greatly missed by all who knew him."