An Afghan policeman opened fire on British soldiers in the volatile southern province of Helmand, killing five before fleeing, British and Afghan authorities said Wednesday, raising concerns about discipline within the Afghan forces and possible infiltration by insurgents.

The attack on Tuesday afternoon came a month after an Afghan policeman on patrol with U.S. soldiers fired on the Americans, killing two. Training and operating jointly with Afghan police and soldiers is key to NATO’s strategy of dealing with the spreading Taliban-led insurgency and, ultimately, allowing international forces to leave Afghanistan.

Attacks such as these will heighten concern about the effectiveness of the Afghan forces.

Lt. Col. David Wakefield, spokesman for the British forces, told Sky News that the soldiers had been mentoring Afghan national police and had been working and living in the police checkpoint in Helmand’s Nad-e-Ali district.

“It is our initial understanding that an individual Afghan policeman possibly acting in conjunction with one other started firing inside the checkpoint before fleeing from the scene,” he said.

A Helmand police official said authorities searched through the night and on Wednesday for the attacker. He said the man had been working as a police officer in the area for three years, and had passed through a police academy in Kandahar. The official, who spoke on conditions of anonymity, said it was unclear what his motives were.

The attacker was on the roof of a police checkpoint and opened fire on the British soldiers, who returned fire. Six other soldiers were wounded, as were two Afghan policemen, NATO forces headquarters in Kabul said in a statement.

NATO said the attack was being investigated by NATO forces and Afghan authorities.

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