A British soldier died as a result of an "insider attack" at his base in Afghanistan, the Ministry of Defence said.
The soldier, from The Royal Scots Borderers, 1st Battalion The Royal Regiment of Scotland, was killed on Sunday while in Patrol Base Shawqat, in the Nad-e Ali district of Helmand province, a spokesman for Task Force Helmand said.
His next of kin have been informed.
Major Laurence Roche, spokesman for Task Force Helmand, said: "I am very sorry to report the death of a soldier from The Royal Scots Borderers, 1st Battalion The Royal Regiment of Scotland, who was shot by an individual wearing an Afghan National Army uniform at his base in the Nad-e Ali district of Helmand province.
"This is incredibly sad news for the battalion and everyone serving in Task Force Helmand. As we mark Remembrance this weekend, our thoughts now turn to the soldier's family and friends whose loss is so much greater than ours".
The insider attack takes to 438 the number of UK service members to have lost their lives since operations in Afghanistan began in October 2001.
The "green-on-blue" death brings the number of British servicemen killed by Afghan soldiers or police to 12 this year, compared to just one in 2011, three in 2010, and five in 2009.
At least 54 international troops have died as a result of such attacks - where Afghans turn their weapons on their coalition colleagues.
News of the killing came after the Queen led the nation in honouring the fallen on Sunday, as the country fell silent to remember its war dead.
In scenes replicated at memorials across the United Kingdom and Commonwealth nations, the monarch laid the first wreath at the Cenotaph to commemorate members of the Armed Forces who died fighting in all conflicts since the First World War.