Updated

A man wearing an Afghan police uniform shot and killed two British soldiers at a checkpoint in southern Afghanistan on Tuesday, international military officials said.

The assault appeared to the be the latest in a string of insider attacks that have threatened the partnership between international troops and the Afghan forces they are trying to train to take over responsibility for the country's security.

A statement from the NATO military coalition said only that the assailant was wearing a police uniform, leaving open the possibility that the attacker was a militant posing as a policeman. The statement did not provide details on the shooting, saying it was being investigated.

The British Ministry of Defense said the attack happened at a checkpoint in Helmand Province's Nahri Sarraj district.

"The loss of these soldiers is a huge blow," Maj. Laurence Roche, a spokesman for British troops in Helmand, said in a statement.

The two killed soldiers were with the 1st Battalion The Royal Gurkha Rifles, he said.

At least 53 international troops have been killed in attacks by Afghan soldiers or police this year, and a number of other assaults are still under investigation, the international alliance has said.

The surge in insider attacks is throwing doubt on the capability of the Afghan security forces to take over from international troops ahead of a planned handover to the Afghans in 2014. It has further undermined public support for the 11-year war in NATO countries.

The attacks have not been limited to members of the NATO-led international coalition. More than 50 Afghan members of the government's security forces also have died this in attacks by their own colleagues.