Kabul, Afghanistan (CNN) -- Three NATO service members were killed Saturday during attacks in Afghanistan, while a fourth died of noncombat-related injuries, according to the International Security Assistance Force. A roadside bomb took the life of one service member in the southern part of the country, while two others were killed in the same region when two attackers wearing Afghan Police uniforms turned their weapons on NATO troops. One of the attackers was killed when NATO forces returned fire, but the other managed to escape and is currently being sought after, ISAF reported. It's not clear whether the attackers were insurgents or Afghan police, said ISAF spokesman Jimmie Cummings. The United States is expected to pull 23,000 troops out of the country by September. That's ahead of a 2014 deadline to fully withdraw from Afghanistan. An undetermined number of U.S. forces will remain in the country past 2014 working as military advisers and counterterrorism forces, but officials have yet to make public for how long.