An Afghan civilian employed at a NATO base in southern Afghanistan has killed three U.S. soldiers, the latest in a spate of rogue attacks in the country that have left seven U.S. troops dead this week.
The NATO-led international coalition, ISAF, said the shooting took place in the Garmsir district of Helmand Province late on August 10.
The man was not wearing a uniform and it remains unclear how he got hold of the weapon.
"A delegation has been dispatched to the area to investigate the case and more detail is yet to be known. The individual who has carried out the incident has been arrested," provincial spokesman Daud Ahmadi told RFE/RL's Radio Free Afghanistan.
Earlier on August 10, an Afghan police commander and several of his men killed three U.S. Marines after inviting them to a dinner to discuss security issues.
The attack also took place in Helmand Province.
And on August 7, two men in Afghan National Army uniforms shot dead another U.S. soldier in the country's east.
ISAF spokesman Brigadier General Gunter Katz said the incidents were isolated.
"Let me clearly say that those incidents clearly do not reflect the overall situation in Afghanistan, where almost 500.000 soldiers and policemen are working together side by side enhancing their trust, enhancing their cooperation, in order to together fight for a better future of this country and to pressure the insurgency," Katz added.
Cases of Afghan police or soldiers turning their guns on their Western colleagues, however, have been on the rise.
NATO calls them "green-on-blue" attacks.
It has recorded 26 such attacks since January in which 34 people have been killed. Last year, there were 21 attacks in which 35 people died.
Some of these killings were claimed by the Taliban, who say they have infiltrated Afghan security forces. But ISAF blames most attacks on stress, personal conflicts, and cultural differences.
"Green-on-blue" shootings have eroded trust between foreign and Afghan forces as NATO prepares to hand over security to Afghan forces by 2014.
The alliance currently has some 130,000 soldiers in Afghanistan who are scheduled to pull out by the end of 2014.
With reporting by Reuters and AFP