Surround with armed forces (7)
I believe the answer is:
besiege
'surround with armed forces' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for besiege that I've seen before include "Surround (town etc) with armed forces" , "Surround (a stronghold)" , "Pester" , "Surround (a place) with hostile intent" , "Enclose, preventing ingress or egress" .)