Silly action of political party, welcoming back international terrorist leaders (5)
I believe the answer is:
antic
'silly action' is the definition.
(antics are silly acts)
'political party welcoming back international terrorist leaders' is the wordplay.
'political party' becomes 'anc' (African National Congress, South African party).
'welcoming' means one lot of letters goes inside another (in sense of 'inviting in').
'back' shows that the letters should be reversed in order.
'leaders' indicates taking the first letters.
The initial letters of 'international terrorist' is 'it'.
'it' backwards is 'ti'.
'anc' going around 'ti' is 'ANTIC'.
'of' acts as a link.
(Other definitions for antic that I've seen before include "Caper; grotesque (arch.)" , "Grotesque, fantastic (archaic)" , "Playful or mischievous act" , "Old clown" , "Absurd action" .)