Angry, thwart the international organisation (3,5)
I believe the answer is:
red cross
'international organisation' is the definition.
(I've seen this before)
'angry thwart' is the wordplay.
'angry' becomes 'red' (someone may go red when angry).
'thwart' becomes 'cross' (synonyms).
'red'+'cross'='RED-CROSS'
'the' acts as a link.
(Other definitions for red cross that I've seen before include "International organisation for treatment of wounded in war" , "International organisation for care of wounded in war" , "that brings relief!" , "organisation offering aid" , "International organisation for helping war-wounded" .)