The agency cited anonymous Afghani military sources as saying that the attack was triggered by an overnight cross-border militant incursion into Afghanistan. The militants are thought to have attacked NATO and Afghan forces. An air strike was then called in, apparently hitting the Pakistani checkpoint by accident.
Exact details on the incident remain unclear and a U.S. military spokesman in Afghanistan refused to comment on the incident.
This would not be the first time that Pakistani soldiers have been killed in so-called 'friendly fire' on the Afghan-Pakistani border.
Pakistan has lodged a protest with the coalition over the air strike, calling it an "unprovoked and cowardly" attack by U.S. forces.
The attack "hit at the very basis of cooperation and sacrifice with which Pakistani soldiers are supporting the coalition in the war against terror", the Pakistani military quoted a spokesman as saying.
Relations between Kabul and Western forces in Afghanistan have been strained of late over Pakistani efforts to strike deals to put an end to militant violence on its side of the border. NATO however maintains that such pacts cause more violence in Afghanistan.
