President Hamid Karzai ordered Tuesday an investigation into the killing of six NATO soldiers by an Afghan police officer in eastern Afghanistan, DPA reported.
Karzai "expressed his regrets" over the incident and asked the Interior Ministry to investigate the killing, the presidential palace said.
A rogue officer turned his weapons on NATO military trainers during an exercise in Chaparhar district of Nangarhar province on Monday, before he was killed by the allied forces.
Taliban militants in an online statement identified the attacker as Azatullah, of Nangarhar province. He had infiltrated the border police force with a mission to target foreign troops, it said.
The Taliban statement claimed that seven soldiers were also injured in the attack.
NATO did not reveal the deceased's nationalities, but an Afghan provincial official who declined to be named said the soldiers were from the United States.
The incident was seen as the latest setback for Afghan forces, who are slated to take responsibility for overall security in the country by the end of 2014.
Earlier this month, NATO leaders decided at a summit in Lisbon to begin the transfer of security responsibility to the local forces starting from June 2011.