The Afghan policeman who killed six American troops had been on the force for three years and had no criminal background, Afghanistan’s interior ministry has said.
The gunman, who also died in the shooting on Monday, opened fire as the group was on its way to a weapons range in Nangarhar province near the Pakistan border.
The Taliban has claimed responsibility for the attack, saying the officer had enlisted as a sleeper agent in order to have an opportunity to kill foreigners.
The bloodshed – which appeared to be the deadliest attack of its kind in at least two years – underscored one of the risks in the programme to train enough recruits to turn over the lead for security to Afghan forces by 2014.
Attacks on Nato troops by Afghan policemen or soldiers, although still rare, have increased as the coalition has accelerated the programme. Other problems with the rapidly growing security forces include drug use, widespread illiteracy and high rates of attrition.
Also on Monday, Afghan gunmen attacked a construction company in Kabul province, wounding one security guard and kidnapping nine others in the mountainous Sarobi district.
Nine other guards escaped the attack. The gunmen also seized several rifles.