Five British soldiers were shot dead by an Afghan policeman at a checkpoint in Helmand province, officials said Wednesday.

"The soldiers were all killed as a result of gunshot wounds sustained in an attack in the Nad-e’Ali district of Helmand Province during the afternoon of 3 November 2009," the UK Ministry of Defence said in a statement. An investigation into the attack is under way.

Military spokesman Lieutenant Colonel David Wakefield told BBC radio the soldiers had been mentoring Afghan police and living inside the checkpoint.

"It would appear... that an individual Afghan national policeman, possibly acting in conjunction with another, started firing within the checkpoint," he said. The policeman reportedly fled the scene after the shooting.

Bloodiest year since the Falklands

The incident brings to 229 the number of British troops who have been killed in Afghanistan.

This year has been the bloodiest for the UK's armed forces since the Falklands campaign in 1982.

Three of the soldiers were from the Grenadier Guards and two from the Royal Military Police.

Prime Minister Gordon Brown said: "The death of five brave soldiers in a single incident is a terrible loss.

"My thoughts, condolences and sympathies go to their families, loved ones and colleagues. I know that the whole country, too, will mourn their loss."