Enemy of international environmental group (3)
I believe the answer is:
foe
This clue is a double definition.
'enemy' is the first definition.
(thesaurus)
'international environmental group' is the second definition.
(Friends of the Earth)
'of' acts as a link.
(Other definitions for foe that I've seen before include "Opposition" , "Environmentalists" , "Am archaic enemy" , "friend never!" , "Antagonist" .)