"The Turkish Armed Forces continue to carry out their duties in the territory within the engagement rules agreed by the guarantor countries in the Astana negotiations".
The convoy included about 30 military vehicles, said Abu Khairo, a commander in a Free Syrian Army (FSA) rebel group based in the area, and it entered Syria near the Bab al-Hawa border crossing, according to a civilian witness.
Vehicles arriving in district of Reyhanli, bordering city of Idlib, were dispatched to border units to be deployed.
President Tayyip Erdogan announced the deployment on Saturday, saying Turkey was conducting a "serious operation" with rebel groups it supports, as part of the Astana "de-escalation" deal.
While Turkey supports Syrian opposition fighters and calls for Assad's ouster, Ankara has worked closely in the last few months with Russian Federation - who supports Assad - in the hope of bringing the war to an end. But since a year ago Ankara has focused on securing its border, both from jihadists and from Kurdish forces that control much of the frontier area inside Syria.
Turkish army armored vehicles drive at the Syria-Turkey border on on October 8, 2017.
One of Turkey's main concerns is the expansion of the Syrian Kurdish People's Protection Units (YPG), which Ankara says is linked to the Kurdistan Workers' Party (PKK) waging an insurgency inside Turkey.
That operation was also aimed at stopping the YPG using its own advances against IS from linking Afrin with the much larger area it controls in northeastern Syria.
A string of ceasefire deals in recent months has eased the fighting in western Syria.
The Turkish army has begun setting up "observation posts" in Syria's northwestern Idlib province in its efforts to create a de-escalation zone, the military said on Friday, although the move was seen partly aimed at containing the Kurdish YPG militia.