Three UK troops killed by renegade Afghan soldier
The soldier used a shoulder-mounted launcher to fire the grenade at the soldiers at around 2am today, and Afghan defense ministry spokesman said.
He escaped and is being hunted.
President Hamid Karzai apologised to the British government, and a joint Nato-Afghan team was investigating the incident in the southern province of Helmand.
Nato commander Gen. David Petraeus called for unity in the fight to bring security to Afghanistan.
"This is a combined, joint mission, Afghan and Alliance troopers fighting shoulder-to-shoulder against the Taliban and other extremists," he said.
"We have sacrificed greatly together, and we must ensure that the trust between our forces remains solid in order to defeat our common enemies."
Last November an Afghan policeman killed five British troops, underlining the difficulty in training the Afghan security forces who are hoped to take on more responsibilities, allowing international forces to return home.