Turkish forces have shot down a Syrian military jet they say was violating their airspace despite warnings.
Turkey’s Prime Minister Recep Tayyip Erdogan warned such action by Syria merited a “heavy response”.
But Syria accused Turkey of “blatant aggression”, saying the plane had been over Syrian territory at the time.
The incident reportedly occurred in an area where Syrian rebels and government forces have been fighting for control of a border crossing.
Turkey and Syria – once allies – share more than 500 miles (800km) of border.
Turkey has broadly sided with the rebels in Syria’s war since October 2011.
Turkish forces launched artillery strikes on Syrian targets in late 2012 after the Syrians shot down a Turkish jet.