The leak features information such as names, addresses and citizenship ID numbers for some 49.6 million people.
The Associated Press was able to partially verify the authenticity of the leak by running 10 Turkish ID numbers against names contained in the leaked data. Eight of them matched.
There are fears that the leak could put people at risk of fraud. Speaking during a visit to Finland, Prime Minister Ahmet Davutoglu said: "Our citizens must be reassured that measures are being taken." He didn't elaborate.