The British military death toll in Afghanistan and Iraq hit 300 when two Royal Marines were killed in an explosion in Helmand province.
The deaths bring the total killed in Afghanistan to 124, while 176 have died on active service in Iraq since operations began.
The marines, from UK Landing Force Command Support Group, were taking part in a joint patrol with soldiers from Afghan security forces when their vehicle was struck by an explosive device in the Garmsir district of Southern Helmand yesterday.
Next of kin have been informed and asked for a 24-hour period of grace before more information is released, the Ministry of Defence said.
Commander Paula Rowe, of Task Force Helmand, said: "This is a tragic blow to us all in the task force, but our loss is nothing compared to that of their families and loved ones.
"Our thoughts and prayers are with them at this terrible time."
The pair were operating as part of Task Force Helmand's Information Exploitation Group, which is responsible for gathering information to improve situational awareness and to gain an advantage over enemy forces.
The incident happened at 4.47pm local time on Wednesday.
The marines were on a routine patrol and the cause of the explosion is not yet known.
Brigadier General Richard Blanchette of the Nato-led International Security Assistance Force (ISAF) said: "Our deepest sympathies go out to their family, friends and fellow soldiers. Their lives are irreplaceable to all of us who fight for the peace and stability of Afghanistan."
