"It is a temporary measure," a Turkish diplomat told reporters, confirming that the Oncupinar gate had been closed. "At this stage, it has been closed as a precaution because of the mobility on the other side of the border."
Kilis Governor Suleyman Tapsiz also said the border gate had been closed to vehicles carrying humanitarian aid.
The Oncupinar border gate in Turkey's Kilis province lies opposite the Syrian Bab al-Salameh gate, only five kilometers from Syria's Azaz.
Fighting between militants of al-Qaeda front group, the Islamic State of Iraq and the Levant (ISIS), and rebels of the Free Syrian Army broke out on Wednesday and continued on Thursday in the town of Azaz.
Recently, clashes between different groups of the Syrian opposition fighters intensified near the Turkish-Syrian border, bringing Turkey to high alert about any spillover into its border cities.