Two Gurkhas have been killed in Afghanistan by a man wearing an Afghan police uniform, in what appears to be the latest "green-on-blue" attack on British troops.
The soldiers, from the 1st Battalion The Royal Gurkha Rifles, were shot dead at a checkpoint in Nahr-e Saraj, Helmand Province.
Their deaths bring the number of British servicemen killed by Afghan soldiers or police to 11 this year, compared to just one in 2011, three in 2010, and five in 2009.
The deaths of a British army medic and a Royal Marine last week, alongside an Afghan man believed to be a policeman but not in uniform, is still under investigation.
At least 53 international troops have died as a result of "insider attacks" - where Afghans turn their weapons on their coalition colleagues.
Major Laurence Roche, spokesman for Task Force Helmand, said: "I am saddened to report the deaths of two soldiers from 1st Battalion The Royal Gurkha Rifles who were shot and killed by a man wearing an Afghan police uniform at a checkpoint in the Nahr-e Saraj district of Helmand Province.
"The loss of these soldiers is a huge blow to The Royal Gurkha Rifles and everyone serving in Task Force Helmand. Our thoughts are with their families, friends and fellow Gurkhas at this time."
The gunman is said to have fled after the shooting and is now being hunted.
The Gurkhas' next of kin have been informed, the Ministry of Defence (MoD) said.
Their deaths take the total number of UK service members to have lost their lives since operations in Afghanistan began in October 2001 to 437.
They come less than a week after army medic Corporal Channing Day and Royal Marine Corporal David O'Connor died in the same district of Helmand Province.
Cpl Day, who served with 3 Medical Regiment, and Cpl O'Connor, of 40 Commando, were injured on patrol with C Company in Nahr-e Saraj last Wednesday. They died alongside an Afghan man who was believed to have been a member of the Afghan Uniformed Police but was not wearing uniform at the time.
An initial review into their deaths revealed the killings were not caused by "friendly fire" but the involvement of the Afghan man led to speculation the incident was another insider attack.
The growing number of British troops losing their lives at the hands of Afghan colleagues has sparked increasing concerns about green-on-blue attacks.
Families of dead servicemen and women have called for an early withdrawal from Afghanistan, speeding up the planned return of all troops.
The current aim is to reduce troop numbers by 500 this year and seek a further drawdown next year ahead of full withdrawal of combat troops by the end of 2014.
But defence chiefs have insisted the attacks should not derail the drawdown process and there should be no "cliff edge" to the reduction of troops.
Damian Collins, Conservative MP for Folkestone and Hythe, said the attacks "undermined" the work British troops were undertaking with the Afghans.
He told BBC Radio Kent: "It is terrible news and everyone in Folkestone will be saddened to hear it.
"The Gurkhas are very much part of our community. We are very proud of the work they have done on a number of tours of duties of Afghanistan since the war, and we will be united in our grief and sense of loss."