The casualty was embedded with US forces fighting Isis when they were caught in a bomb blast on Thursday.
The spokesperson gave no information regarding the casualty’s service branch, unit or gender.
He said: “It is with regret that we must confirm that a member of the UK Armed Forces was killed by an improvised explosive device in Syria yesterday.
“The individual was embedded with US forces on a counter-Daesh operation when the incident occurred.
“The family has been notified and our thoughts are with them at this difficult time.”