A Royal Air Force airman and a soldier from 1st Battalion Welsh Guards were killed 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 with local officials when two people wearing Afghan Police uniforms opened fire.
Defence Secretary Philip Hammond said yesterday 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 told BBC1’s The Andrew Marr Show.
He added: “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.
“We don’t yet know what the motive was, we don’t yet know whether this was an insurgent who’d infiltrated the police or whether it was a policeman who simply had a grievance of some kind.
“This is a society where people traditionally settle grievances by violence.”
Major Ian Lawrence, spokesman for Task Force Helmand, said: “Sadly, it is my duty to confirm that a soldier serving with 1st Battalion Welsh Guards and an airman from The Royal Air Force have been shot and killed in the Lashkar Gah district of Helmand province.
“The thoughts and condolences of everyone serving in the Task Force are with their families and friends.”
Next of kin have been informed.
The incident on Saturday appears to be the latest in a string of “green on blue” attacks in which members of the Afghan security forces have opened fire on international 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 province. 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 later claimed responsibility.
The victims were Warrant Officer Class 1 Darren Chant, 40, from Walthamstow, London, Sergeant Matthew Telford, 37, from Grimsby, and Guardsman Jimmy Major, 18, also from Grimsby, all members of 1st Battalion The Grenadier Guards. Royal Military Policemen Corporal Steven Boote, 22, from Birkenhead, and Corporal Nicholas Webster-Smith, 24, from Brackley, Northamptonshire, were also killed.
Such attacks have become increasingly common in recent months, particularly since the burning of copies of the Koran at a US base in February.
A total of 414 members of UK forces have died since operations in Afghanistan began in October 2001.