The killing -- which local police said was by an Afghan recruited just five days earlier to a village defense force -- is the sixth similar incident in two weeks.
The shooting happened in the far western province of Farah, said Jamie Graybeal, a spokesman for the international coalition force. The attacker was a member of the Afghan Local Police, a village defense force that is being trained by international forces, including U.S. special forces.
Graybeal says two American service members died before the Afghan attacker was shot and killed.
The attack came at about 8 a.m. Friday after the U.S. forces arrived in the village of Kinisk to train members of the local police, Farah provincial police chief Agha Noor Kemtoz said. He identified the attacker as Mohammad Ismail, a man in his 30s who had been recruited to the program five days ago.
He said one Afghan National Police officer was seriously wounded in the shooting.
Attacks by Afghan allies on international troops have escalated this year, killing at least 36 foreign troops and raising questions about the strategy to train national police and soldiers to take over security and fight the Talbian after most foreign troops leave by the end of 2014.