The 100th British member of the Armed Forces to die this year after being deployed to Afghanistan is expected to be named by the Ministry of Defence on Thursday.
The soldier, from 1st Battalion Irish Guards, died from a gunshot wound received during an ambush by insurgents on Wednesday in the Nahr-e Saraj district of Helmand Province.
It brings the number of British military personnel to die on duty or returning from theatre in the war-ravaged country into triple figures.
The latest death follows that of two others in November. Earlier this month, Senior Aircraftman Scott Hughes, 20, from North Wales, died in a boating accident in Cyprus as he was returning home following a tour of duty in Afghanistan.
His death has been included by the Ministry of Defence in their official tally of casualties resulting from the conflict.
A further fatality was recorded in Afghanistan on Remembrance Sunday.
In all, some 345 UK military personnel have died since operations in Afghanistan began in 2001.
Commenting on the latest incident, Lieutenant Colonel David Eastman, spokesman for Task Force Helmand, said: "The soldier was carrying out vital work mentoring an Afghan National Army patrol, in order to develop their ability to protect the people of Nahr-e Saraj (North), when he was struck by small arms fire.
"In carrying out this crucial role he gave his life so that others might hope for a better future. Our thoughts are very much with his family and friends at this deeply sad time."