Serbia confused with one part of Russia (7)
I believe the answer is:
siberia
'part of russia' is the definition.
('Siberia' is part of 'russia')
'serbia confused with one' is the wordplay.
'confused with' indicates an anagram.
'one' becomes 'i' (Roman numeral).
'serbia' anagrammed with 'i' gives 'SIBERIA'.
(Other definitions for siberia that I've seen before include "Large E. Russian region" , "Arctic region" , "Region in former USSR noted for harsh winters and notorious for prison camps" , "Cold area" , "Frozen region of former USSR noted for prison camps" .)