The Ministry of Defence has confirmed a 20-year-old marksman killed six members of the Taliban with a single bullet.
"The guy was wearing a vest. He was identified by the sniper moving down a tree line and coming up over a ditch," Lt Col Slack said.
"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."
The same sniper, who remains unnamed, killed a Taliban machine-gunner with the first shot on his tour of duty from 1,340m away.
The incidents have been disclosed as Britain continues to move towards the withdrawal of all combat soldiers from Afghanistan by the end of this year.