Russia’s violation of Turkish airspace over the weekend “does not look like an accident”, Nato has said.
Secretary-General Jens Stoltenberg said Russia had not provided “any real explanation” of the violation, which “lasted for a long time.”
Russia says Saturday’s incursion was brief and due to bad weather.
It is examining claims of another violation.
Turkey’s army also says an unidentified fighter jet locked its radar on to eight of its jets on Monday.
It echoes a similar incident on Sunday, when an unidentified Mig-29 – which analysts say may have been Syrian – locked its radar onto Turkish jets for more than five minutes over the Turkish-Syrian border.
Missile systems inside Syria were also locked on to Turkish planes for more than four minutes on Monday, the Turkish military says.
