An Afghan soldier attacked his coalition allies with gunfire and a rocket-propelled grenade early Tuesday, killing three British troops and wounding four more.
The Taliban claimed the soldier then fled to an insurgent-controlled area, surrendered to them and was taken to a "safe place." The account could not be independently confirmed.
The Afghan soldier was assigned to a patrol base shared by NATO troops and the Afghan National Army in the volatile southern province of Helmand.
Helmand is where American troops mounted a large-scale offensive earlier this year to uproot Taliban insurgents from a stronghold in the town of Marja.
The motive for the attack in the Nahr-e-Sarraj district, home to members of the 1st Battalion Royal Gurkha Rifles, remained unclear, but it could prove deeply embarrassing for the Afghan government and U.S. military leaders, who have stressed the importance of ratcheting up the training of Afghan security forces to gradually take on more responsibility for securing their own country.
Defense Minister Liam Fox called the attack "a despicable and cowardly act." But he said training Afghan security forces would continue because it is "vital to the international security mission in Afghanistan, and today's events will not undermine the real progress we continue to make."
With Tuesday's incident, 317 British soldiers have been killed in Afghanistan since 2001, according to icasualties.org, an independent website that tracks war-related deaths in the Afghan conflict.
It was the second time in eight months that an Afghan turned against British troops partnering with local security forces. In November, an Afghan policeman killed five British soldiers at a checkpoint — also in southern Helmand province, where Tuesday's attack happened. Afghan police in the past have also attacked American soldiers and their own police stations, though such intentional attacks are rare.
The speed with which Afghan security forces are growing — the allies set an interim goal of expanding the Afghan army from 85,000 in 2009 to 134,000 troops by 2011 — has raised concerns about infiltration by the Taliban and the professionalism of the recruits. The police force is facing similar challenges.
Elsewhere in Afghanistan, border police seized more than 50 tons of ammonium nitrate, the main component in Taliban-made roadside bombs that have become the leading killer of U.S. and Western troops in the country.
Information from the Los Angeles Times was used in this report.