Islamic republic on the Persian Gulf (4)
I believe the answer is:
iran
'islamic republic on the persian gulf' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for iran that I've seen before include "Country where the official language is Farsi" , "Modern-day Persia" , "Persia some time ago" , "Farsi-speaking country" , "Persia today" .)