Umarali Kuvvatov, who was an outspoken critic of Tajikistan's veteran President Emomali Rakhmon, was killed by a single shot to the head at on Thursday around 10.30pm (2030 GMT) local time in Istanbul's Fatih district.

He was already dead when medics arrived at the scene, Turkish media said, which first reported on the murder on Friday.

News agency Dogan said that Turkey's anti-terrorism police unit and murder squad were leading the investigation, and said the 47-year-old had been eating dinner at a house in the area prior to the crime.

Kuvvatov, head of the "Group 24" opposition movement, was living in exile in Turkey after Tajikistan's Supreme Court declared the movement an extremist organization in October last year.

Tajik officials say Kuvvatov was wanted on charges including extremism, economic infringements and hostage-taking, but Turkey had refused to extradite him.

He had fled Tajikistan in 2012, and been living with his family in Istanbul since 2013.

an/kms (Reuters, AFP)