Two British soldiers shot dead by a rogue Afghan policeman have been named as Sergeant Gareth Thursby and Private Thomas Wroe.
The two men - both of 3rd Battalion The Yorkshire Regiment - were shot at a checkpoint in the Nahr-e-Saraj district of Helmand Province.
They were killed by a man dressed as an Afghan policeman who pretended to be injured so they would help him, defence sources said.
Defence Secretary Philip Hammond said: "I was saddened to hear of this cowardly act by a man wearing an Afghan local police uniform, which has taken the lives of two brave British soldiers.
"All of our thoughts are with the families of Sergeant Gareth Thursby and Private Thomas Wroe. They gave their lives protecting Britain's national security, helping to make sure that Afghanistan never again becomes a haven for international terrorism."
Sgt Thursby, 29, from Skipton, North Yorkshire, leaves his wife, Louise, and two children, Joshua and Ruby.
Lieutenant Colonel Zachary Stenning MBE, Commanding Officer, 3 Yorks, said: "We have lost one of our finest, Sergeant Gareth Thursby.
"His nickname 'Bull' epitomised everything; he was strong, confident and unbelievably robust. He was admired and deeply respected by his soldiers and peers for his soldiering skills, physical strength and forthright honesty. Utterly professional, his standards were legendary.
"When there were dangerous moments, it was always Sergeant Thursby who could be found at the front, offering steadying words to his Platoon Commander and the young soldiers. Such dedication and indeed selfless love for his fellow soldiers is remarkable and testament to the qualities of this unique man."
Pte Wroe, from Holmfirth, West Yorkshire, joined the British Army two years ago. He was deployed to Afghanistan on July 1, shortly after his 18th birthday.
Lt Col Stenning described Pte Wroe as "always eager".
He said: "Arriving only some two months ago, his energy and professionalism quickly earned him the respect of his fellow team members. But it was his humour and character that really stood out. Whenever anyone asked how he was, his consistent reply was 'always happy'.
"This phrase captured the young man Wroe was. On patrol his professional skills were impressively high given his relative inexperience. When back in the isolated checkpoint, his humour and vibrancy shone through and energised those around him."
Pte Wroe's parents, Michael and Claire, and sister Demi said in a statement: "We can't believe you have been taken so soon from us. You will always be in our hearts for ever and ever.
"You would light up the room with your smile and bubbly personality. Our world will be a duller place without you. We are so proud of you son, on all you achieved and we are grateful for every special thing you gave us. We will always love you Tom."
Earlier, tributes were paid to another British soldier who was killed in the Nahr-e Saraj district on Friday when his vehicle hit a roadside bomb.
Fijian-born Lance Corporal Duane Groom was described by friends as a "fearless and fantastic" soldier.