The next of kin have been told but the marine's name has not been released.
In western Afghanistan, one Spanish female soldier was killed and two other troops were wounded when a convoy of armoured ambulances came under attack.
Colonel Ian Huntley, Acting Commander of the UK Task Force in Afghanistan, announced the death of the British marine with "deep regret".
"Whilst the loss of a valued colleague is a severe blow, our immediate thoughts and prayers are with his family and friends, whose anguish must be immense," he said.
"Our heartfelt condolences go out to them.
"This loss, though tragic, will not deflect us from our mission, rather it hardens our resolve."
The total number of UK troops killed while on operations in Afghanistan since 2001 has now risen to 47.
The attack on the Spanish forces is believed to have occurred when they struck a powerful mine in the western town of Shindand.
The soldiers were travelling in one of five armoured vehicles supporting Italian forces, a statement from the Spanish Defence Ministry said.
It added it expected the two male soldiers hurt in the blast to survive.
THE ONLY FILTH IS YOU AND THE LIKES OF YOU, YOU FUCKING BASTARD.
GO BACK TO YOUR FILTHY GOAT FUCKING COUNTRY.
FUCK YOU AND ALL YOU FILTHY ARABS AND MUSLIMS.
SJ
A nuclear attack on Waziristan would solve a lot of problems.
Iamhere
ACTUALLY THEY SHOULD NUKE ALL OF THOSE FUCKING MUSLIMS AND ARABS