Balkan region rejected Spain's objectionable claims (6)
I believe the answer is:
bosnia
'balkan region' is the definition.
(I've seen this in another clue)
'rejected spain's objectionable claims' is the wordplay.
'rejected' says the letters should be written in reverse.
'claims' indicates the answer is hidden within the clue (the answer is held or claimed within the clue).
'ainsob' can be found hidden inside 'spains objectionable'.
'ainsob' written backwards gives 'BOSNIA'.
(Other definitions for bosnia that I've seen before include "European country, capital Sarajevo" , "Balkan state" , "Central European country" , "Balkan region joined with Herzegovina" , "No bias (anag)" .)