The marines, from UK Landing Force Command Support Group, were taking part in a joint patrol with soldiers from Afghan security forces when an explosive device in the Garmsir district of Southern Helmand struck their vehicle on Thursday. The Ministry of Defence said that next of kin have been informed and asked for a 24-hour period of grace before more information is released.
"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," said Commander Paula Rowe of Task Force Helmand.
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 4.47 pm local time on Thursday, Nov 13
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."
On November 4 the first Nepalese Gurkha soldier was killed fighting in the country.
Yubraj Rai, 28, who served with the 2nd Battalion The Royal Gurkha Rifles, was killed while on patrol near Musa Qaleh in southern Afghanistan.