British Maj.-Gen. Nick Carter, centre, answers journalists' questions with Afghan police commander Mir Wais Norzai, left, and Afghan Army Gen. Sher Mohammad Zazai at the British base in Lashkar Gah, Afghanistan, on Wednesday. (Abdul Khaleq/Associated Press)

An Afghan policeman opened fire on British soldiers in the volatile southern province of Helmand, killing five, British and Afghan authorities said Wednesday.

The incident came almost exactly a month after an Afghan policeman on patrol with U.S. soldiers opened fire on the Americans, killing two before fleeing.

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.

Former foreign minister Abdullah Abdullah, who was the main challenger to President Hamid Karzai in Afghanistan's recent fraud-marred election, said the continuing violence showed that the Karzai administration had failed to bring peace to the country despite assistance from international forces.

The five British soldiers were killed in Helmand's Nad-e-Ali district on Tuesday afternoon, Britain's Defence Ministry said, bringing the total number of British forces personnel who have died in Afghanistan to 229. Britain has 9,000 troops in the country.

"The soldiers concerned were mentoring Afghan national police. They were working inside and living inside an Afghan national police checkpoint, just outside Nad-e-Ali district centre," Lt.-Col. David Wakefield, spokesman for the British forces, told Sky News. "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."

Motives unclear

NATO said the attacker's motives were unclear, and that the incident was being investigated by Afghan authorities and Britain's Royal Military Police.

A British soldier and an Afghan police officer work together to secure an area in August. (Ahmad Masood/Reuters)

In London, British Prime Minister Gordon Brown extended his condolences to the soldiers' families.

"The death of five brave soldiers in a single incident is a terrible loss," he said. "They fought to make Afghanistan more secure, but above all to make Britain safer from the terrorism and extremism which continues to threaten us from the border areas of Afghanistan and Pakistan."

Brown insisted he remained committed to ensuring his country's troops had "the best possible support and equipment — and the right strategy, backed by our international partners, and by a new Afghan government ready to play its part in confronting the challenges Afghanistan faces."

Last year over a period of less than a month, Afghan policemen twice attacked American soldiers in the east of the country. In October 2008, a policeman threw a grenade and opened fire on a U.S. foot patrol, killing one soldier, while the previous month, an officer opened fire at a Paktia police station, killing a soldier and wounding three before he was fatally shot.