"We are focusing on the possibility of an attempt (coup)," Yildirim said. "There was an illegal act by a group within the military that was acting out of the chain of military command. Our people should know that we will not allow any activity that would harm democracy."
The Dogan news agency says one-way traffic on the Bosporus and Fatih Sultan Mehmet bridges were blocked.
Video footage showed the bridge being blocked by military vehicles.
