Syria demanded on Saturday that Turkish troops who had entered northwestern Syria leave immediately, saying their presence constituted a "flagrant aggression".
A Foreign Ministry statement carried on state media said the entry of Turkish military vehicles into rebel-held northwest Syria through the Bab al-Hawa crossing late on Thursday was a violation of international law.
Turkey says it is operating alongside Syrian rebel groups to implement a deal reached last month with Russia and Iran in Kazakhstan to reduce fighting between insurgents.