A serviceman from 40 Commando Royal Marines was killed in an explosion in Afghanistan, the Ministry of Defence said today.
The marine died last night in a blast in the Sangin District of Helmand Province.
He is the 301st serviceman killed in the conflict.
Next of kin have been informed.
The marine had been on a reassurance patrol to improve security in the local area shortly before he was caught in the blast.
Spokesman for Task Force Helmand Lieutenant Colonel James Carr-Smith said: "It is with deep sadness I must inform you that a marine from 40 Commando Royal Marines was killed in Sangin last night.
"He had recently returned from a patrol when he was killed by an explosion.
"He had been improving the lives of local Afghans and helping to protect them from the insurgency.
"He died a marine. He will be greatly missed and his sacrifice will not be forgotten. We will always remember him."
The 300th member of British forces to die in the Afghan war will be named later today.
The Royal Marine, also from 40 Commando, died from his wounds in the Queen Elizabeth Hospital in Birmingham on Sunday morning with his family by his side.
He was injured in a blast in the Sangin district eight days earlier.
Major Renny Bulmer, spokesman for 40 Commando, based in Taunton, Somerset, said: "Our thoughts are with his immediate family, who were with him at the hospital.
"His courage and sacrifice will not be forgotten. We will remember him."
He was the 55th UK fatality this year and the seventh member of 40 Commando killed since the Royal Marines took command of the notoriously violent Sangin area in April.
Prime Minister David Cameron led tributes to the sacrifices made by the 300 British servicemen and women who have died since operations in Afghanistan began in October 2001.
He said: "It is desperately sad news. Another family with such grief and pain and loss.
"Of course the 300th death is no more or less tragic than the 299 that came before.
"But it is a moment, I think, for the whole country to reflect on the incredible service and sacrifice and dedication that our armed services give on our behalf.
"We are paying a high price for keeping our country safe, for making our world a safer place, and we should keep asking why we are there and how long we must be there."
The UK currently has about 10,000 troops in Afghanistan, of whom 8,000 are based in Helmand, the country's most dangerous province.
Since becoming Prime Minister, Mr Cameron has stressed that British forces will not remain in Afghanistan "a day longer than is necessary".
Defence Secretary Liam Fox said British forces in Afghanistan were protecting the UK's national security.
"Their efforts will bring security and stability to Afghanistan and prevent it from once again becoming a base from which terrorists can attack the UK and our allies around the world," he said.
Opponents of the war repeated calls for UK forces to be brought home.
Lindsey German, convenor of the Stop the War Coalition, said: "It is no surprise that there is an escalating death rate, among British and other Nato troops as well as Afghans, so this day should be one for reflection for our Government.
"Instead of intensifying the war, the Government should admit it cannot win. This war is unpopular with Afghan people as well as the British public."
The anti-war group will demand the withdrawal of UK forces from Afghanistan in a protest outside Downing Street today to coincide with Chancellor George Osborne's emergency Budget.Reuse content