A 20-year-old Army sniper killed six Taliban fighters with a single bullet when the shot hit the trigger switch of a suicide bomb vest, according to a report.

The shot, made at a range of 850 metres, was fired by a lance corporal in the Coldstream Guards in Kakaran, southern Afghanistan, in December but has only just come to light.

Lt Col Richard Slack, commanding officer of 9/12 Royal Lancers, described what happened as British and Afghan troops engaged about 15 to 20 Taliban fighters.

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“The guy was wearing a vest. He was identified by the sniper moving down a tree line and coming up over a ditch,” he told The Daily Telegraph. “He had a shawl on. It rose up and the sniper saw he had a machine gun.

“They were in contact and he was moving to a firing position. The sniper engaged him and the guy exploded.

“There was a pause on the radio and the sniper said, 'I think I’ve just shot a suicide bomber’. The rest of them were killed in the blast.”

A second suicide vest with 20kg of explosives was found nearby.

The same sniper also shot a Taliban machine gunner at a range of 1,340 metres.