A Royal Marine was killed in Afghanistan after a grenade was thrown into his patrol's checkpoint, the Ministry of Defence said.
The serviceman, from 42 Commando Royal Marines, died in hospital after the attack in the Nad-e Ali district of Helmand province yesterday.
The family of the Marine, who is expected to be identified today, has been told.
His foot patrol initially came under attack by insurgents using small arms.
It fired back and also used used mortars and air support to fight off their attackers.
The servicemen then returned to the checkpoint and were preparing to redeploy when insurgents attacked again.
A grenade landed in the checkpoint which wounded the Marine. He was taken to the military hospital in Camp Bastion but died later, the Ministry of Defence said.
Task Force Helmand spokesman Major Rolf Kurth said: "The Royal Marine was part of a foot patrol deployed to reassure local residents, and deter and disrupt insurgent activity, when they came under small arms attack.
"With the help of mortars and close air support, they broke contact with the insurgents and returned to their check point. They then came under further attack, and the Royal Marine was mortally wounded by a grenade that landed inside the check point.
"He died later in Camp Bastion Role 3 Hospital. Our thoughts and prayers are with his family and friends in their time of grief."
More than 320 troops in the Nato coalition have been killed in Afghanistan this year alone.
The total number of British service personnel who have died since operations began in Afghanistan in 2001 is now 378.