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 Tuesday afternoon came a month after an Afghan policeman on patrol with US 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. 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 condition his name not be used because of the sensitivity of the situation, 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. The British fatalities were among the largest in a single incident in Afghanistan. – AP They brought the total number of British forces who have died in Afghanistan to 229. Britain has 9,000 troops in the country, the second largest force after the United States. Last month, British Prime Minister Gordon Brown announced plans to increase troop numbers by 500. Presidential spokesman Humayun Hamidzada said it was an isolated attack. “These are incidents that can happen anywhere. The crazy man who has done this has also attacked the Afghan police,” he told the AP. “You can't use this isolated incident to say that there is a problem with the police force of Afghanistan. In the U.S., people shoot up people in a shopping mall. There are crazy people everywhere.” Karzai issued a statement condemning the killings and offering condolences to the people of Britain and the relatives of the soldiers. The commander of international forces in Afghanistan, Gen. Stanley McChrystal, said he discussed the shooting with Interior Minister Mohammad Hanif Atmar, who “gave me his assurance that this incident will be fully and transparently investigated.” “We will not let this event deter our resolve to building a partnership with the Afghan National Security Forces to provide for Afghanistan's future,” he said in a joint statement issued by NATO forces and the ministry.