Five British soldiers have been shot dead in Helmand Province, in an attack the UK military says was carried out by a "rogue" Afghan policeman.

Three of the soldiers were from the Grenadier Guards and two were from the Royal Military Police. The policeman opened fire within a training compound, where the troops were mentoring Afghan National policeman, before fleeing, Lt Col David Wakefield said. An investigation into the attack is under way.

The prime minister said that the dead men "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.

"I pay tribute to their courage, skill and determination. They will never be forgotten."

The BBC's Ian Pannell says that there are still open questions about both the incident and the motivation for the attack adding that the Afghan National Police have been regarded as a source of difficulty, being accused by some of a lack of professionalism, drug-taking and extracting bribes.