A Royal Marine from 40 Commando died today during a fire-fight with insurgent Afghan forces - the fourth to be killed in four days, the Ministry of Defence said.
The marine was conducting a security patrol in the Sangin district of Helmand Province when he was shot this morning.
Lieutenant Colonel James Carr-Smith, spokesman for Task Force Helmand, said: "He was on a security patrol, helping to better the lives of ordinary Afghans, when he was killed by small arms fire from insurgent forces.
"His courage in the face of danger and his selfless commitment will not be forgotten. He will be deeply missed by all who knew him. We will remember him."
A Ministry of Defence spokesman said the marine, serving as part of Combined Force Sangin, was conducting a security patrol to reassure local nationals in the area around the patrol base when the fire-fight occurred.
His next of kin have been informed.
The announcement came just hours after a Royal Marine killed in an explosion in Afghanistan on Monday was named as Paul Warren, 23, from Leyland, in Lancashire.
A Royal Marine who died yesterday following a fire-fight in Sangin is expected to be named later today.
Marine Richard Hollington became the 300th British serviceman to die since the conflict began when he lost his fight for life on Sunday at the Queen Elizabeth Hospital in Birmingham, eight days after he was critically wounded in an explosion in the Sangin district.
In a statement, Marine Warren's family said he had made them proud, adding: "His cheeky smile will be missed by all who knew him."
Lieutenant Colonel Paul James, the Commanding Officer of 40 Commando Group, described him as "one of life's greats" who had inspired others through his example.
He served with 45 Commando in Afghanistan in 2008/9 and was deployed again in March this year as part of Charlie Company, 40 Commando.
Lt Col James said: "His experience was invaluable in preparing and, at times, reassuring the men."
Marine Warren volunteered to be the Point Man, leading the way during his section's patrols in Sangin, and colleagues spoke of his bravery.
Major Ed Moorhouse, Officer Commanding Charlie Company, said those "on point" were "the bravest of the brave" but to Marine Warren it was his duty to volunteer although he knew the risks.
The father of the first of the four marines to die said today he wanted a personal explanation from the Prime Minister about why Britain is fighting in Afghanistan.
Robin Hollington, father of 23-year-old Marine Hollington, from Petersfield, Hampshire, told ITV News: "I do not see a huge amount of progress being made and it would be extremely interesting to hear from Mr (David) Cameron or Mr (Liam) Fox exactly why we are there because I don't think the public are being told enough to justify what is going on at the moment."
Mr Hollington said he did not think soldiers in Afghanistan were fighting for Queen and country, but for each other.
"They are doing it because, by looking after each other, they have the best chance of coming back alive," he said.