Neighbor of Turkmenistan (4)
I believe the answer is:
'neighbor of turkmenistan' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iran that I've seen before include "Middle East Islamic republic" , "Tehran is its capital" , "Rain (anag) - country" , "Country of western Asia" , "Islamic republic on the Persian Gulf" .)