Afghan gunmen attacked a construction company in Kabul province, wounding one security guard and kidnapping nine others, the Interior Ministry has said.
Gunmen opened fire on 18 Afghan guards in the mountainous Sarobi district, about 27 miles east of the capital, Kabul.
Nine guards were kidnapped and nine escaped, said Zemeri Bashary, a spokesman for the Afghan Interior Ministry.
The gunmen also seized several rifles.
The attack came on the same day that an Afghan border policeman killed six American servicemen during a training mission, underscoring one of the risks in a US-led programme to educate enough recruits to turn over the lead for security to Afghan forces by 2014.
The shooting in a remote area near the Pakistani border appeared to be the deadliest attack of its kind in at least two years.
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.