Designed poster covering international response (7)
I believe the answer is:
riposte
'response' is the definition.
(I know that riposte is a type of response)
'designed poster covering international' is the wordplay.
'designed' is an anagram indicator (designed with the letters).
'covering' means one lot of letters goes inside another.
'international' becomes 'i' (abbreviation eg in IMF).
'poster' with letters rearranged gives 'rposte'.
'rposte' going around 'i' is 'RIPOSTE'.
(Other definitions for riposte that I've seen before include "Quick sharp reply" , "Poster I alter for repartee" , "Sharp answer" , "Fencing counterattack" , "Return thrust or repartee" .)