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.

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 service personnel killed by Afghan soldiers or police to 11 this year, compared to just one in 2011 and three in 2010.

At least 53 international troops have died as a result of "insider attacks" – where Afghans turn their weapons on 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.

"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."

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 said.

Their deaths take the total number of UK service personnel to have lost their lives since operations 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 area of Helmand.

Cpl Day, who served with 3 Medical Regiment, and Cpl O'Connor, of 40 Commando, were injured on patrol with C Company last Wednesday.

They died alongside an Afghan man who was believed to have been a member of the Afghan Uniformed Police.