The Istanbul police department together with teams from the anti-terrorism branch launched the operation at 05:00 local time (02:00GMT), Dogan News Agency said.
Witnesses on Twitter said they heard intensive gunfire and heavy artillery.
Helicopters and armored vehicles have reportedly been deployed in at least three of the city’s neighborhoods. Ankara introduced a curfew in several areas of the city at 07:00 local time (04:00 GMT), according to media reports.
Photos posted on social media show military vehicles rumbling through deserted streets of the city.