The U.S. military confirmed Thursday morning that a man wearing an Afghan police uniform killed two U.S. troops in the Uruzgan province.
It's not clear if the attacker was an enlisted police officer or an insurgent in disguise. The assailant escaped after killing the service members while they were out on a late morning patrol.
The surge in so-called insider attacks is throwing doubt on the ability of the country's security forces to take over after the planned handover to Afghans in 2014.
Before Thursday's assault, 53 foreigners attached to the U.S.-led coalition had been killed in insider attacks from Afghan soldiers or police so far this year, according to the NATO military coalition.
The Taliban have said they are using the attacks as a specific strategy to drive a wedge between the international coalition and the Afghans.
"Increase your efforts to expand the area of infiltration in the ranks of the enemy," Mullah Mohammad Omar urged in a statement. "Jihadist activities inside the circle of the state militias are the most effective stratagem."
The Associated Press contributed to this report.