Turkey has warned Russia against violations of its airspace amid claims Moscow's warplanes have been straying over the border from Syria, as NATO called an emergency meeting over the "unacceptable" intrusion.
Ankara, a NATO member, protested to Moscow on Monday after its F-16 jets intercepted a Russian fighter plane that violated its air space near the Syrian border over the weekend, forcing it to turn back.
Two Turkish jets were also harassed by an unidentified MIG-29 on the Syrian border, Turkey's army said.
"Our rules of engagement are clear whoever violates our air space," Turkish Prime Minister Ahmet Davutoglu told Haber-Turk television.
"The Turkish Armed Forces are clearly instructed. Even if it is a flying bird, it will be intercepted," he added, but played down the idea of "a Turkey-Russia crisis".
"Our channels with Russia remain open," he said, hoping that Moscow would give up on "wrong attitudes".
Foreign Minister Feridun Sinirlioglu contacted his Russian counterpart, Sergei Lavrov, warning him not to repeat similar incidents.
NATO chief Jens Stoltenberg, meeting with Sinirlioglu in Brussels, criticised the "unacceptable violations of Turkish airspace by Russian combat aircraft".
"I call on Russia to fully respect NATO airspace and avoid escalating tensions with the alliance," Stoltenberg said.
Stoltenberg said ambassadors from NATO's 28 member states would meet in the North Atlantic Council later on Monday to discuss the situation.
Turkey and Russia remain on opposing sides of the Syrian conflict, with Moscow one of the few allies of President Bashar al-Assad while Ankara backs a solution excluding the embattled leader.
Russian warplanes have been flying over Syrian territory since Wednesday, conducting air strikes on what Moscow says are IS group targets in the country's northern and central provinces.
The strikes have been criticised by opposition backers like the United States, which leads a coalition already carrying out raids against IS in Syria.
A US official said on Monday the Russian airspace violation was probably deliberate.