Turkey’s PM has denounced an “illegal action” by a military “group”, with bridges closed in Istanbul and aircraft flying low over the capital, Ankara.
Binali Yildirim said the military action was not authorised but it was not a coup. He said that the government remained in charge.
Traffic has been stopped from crossing both the Bosphorus and Fatih Sultan Mehmet bridges in Istanbul.
There are reports of gunshots in the capital Ankara.
Tanks are also said to be stationed outside Istanbul airport.
Mr Yildirim told NTV television by telephone: “We are working on the possibility of an attempt. We will not allow this attempt.” He did not elaborate.
“Those who are in this illegal act will pay the highest price,” he added, saying it would not be correct to describe the move as a “coup”.