Two British servicemen have been shot dead by members of the Afghan Police Force.

A Royal Air Force airman and a soldier from 1st Battalion Welsh Guards were killed on Saturday at a patrol base in the Lashkar Gah district of Helmand province, the Ministry of Defence said.

The servicemen were providing security for a meeting when two people in Afghan Police uniforms opened fire.

Defence Secretary Philip Hammond said it appeared that two assailants were involved in the attack.

"What appears to have happened is that an Afghan police officer opened fire on a mentoring team working with the Afghan police. One of the assailants was killed, we think, by other Afghan police officers, one escaped," he said.

He said: "British forces work alongside Afghan forces every day with thousands of contacts with them every day. This is a country that has an insurgency going on in it and, sadly, occasionally, these events occur."

The incident appears to be the latest "green on blue" attack in which members of the Afghan security forces have fired on their allies.

In March, Sergeant Luke Taylor, of the Royal Marines, and Lance Corporal Michael Foley, of the Adjutant General's Corps (Staff and Personnel Support) were shot dead by an Afghan soldier at the entrance to the UK headquarters in Helmand.

Five British soldiers were killed by a rogue Afghan policeman in November 2009. The gunman opened fire on the men in a military compound in Nad e-Ali before fleeing. The Taliban claimed responsibility.

A total of 414 members of UK forces have died since operations in Afghanistan began in October 2001.