A statement said the incident, which occurred Monday, was under investigation and released no further details. U.S. officials in Washington, speaking on condition of anonymity because the details have not been formally released, confirmed that the victim was not an American.
An Afghan military spokesman in the southern province of Helmand, the most violent in the country, said the attack occurred in the province's Gereshk District. Ghulum Rasool Zazai said a joint commission of Afghan and NATO officers were investigating the assault, and attempting to determine whether the killer was a member of the Afghan National Army.
Several similar attacks have occurred in Gereshk. Last October, two British soldiers were killed by an Afghan policeman. The same month a police officer, along with militants, poisoned their colleagues and shot others, leaving six Afghans dead.
Killings by uniformed Afghans of foreign soldiers and civilians rose dramatically last year, eroding confidence between the sides at a crucial turning point in the conflict. So-called insider attacks killed 61 people in 45 incidents last year compared to 35 killed in 21 attacks a year earlier, according to NATO. This tally does not include the Dec. 24 killing of an American civilian adviser by a female member of the Afghan police because an investigation of the reportedly mentally unstable woman is continuing.
In some cases, militants have donned Afghan army or police uniforms to attack foreign troops. And a number of attacks have also been carried out by members of Afghan security forces against their own comrades.
The attacks come as NATO and Afghan forces are in more intimate contact, with foreign troops handing over security to the Afghans and continuing to train them prior to an almost total withdrawal by the end of 2014. The U.S. will retain a residual force in Afghanistan past that date, the exact number of which is now being determined in Washington.