Ankara said on Friday the Turkish forces in the region were carrying out their duties in line with rules of engagement agreed on with Moscow and Tehran.
Turkey said on Saturday it was carrying out a military operation in Idlib and surrounding areas as part of a deal it reached with Russian Federation and Iran last month to enforce a "de-escalation" zone in northwest Syria.
It did not elaborate on the size of the deployment.
"The allied Turkish armed forces have entered Syrian territory and begun setting up observation posts", Mustafa Sejari, an official in the so-called Free Syrian Army (FSA) rebel group, was quoted as saying by Reuters.
Turkish soldiers, including special forces, and 30 armored vehicles entered Idlib on Thursday night as part of de-escalation zones deal.
Several Turkish military vehicles, ambulances and tankers were visible in photographs published by Turkey's Anadolu news agency late on Thursday stationed at a village near Turkey's Reyhanli border gate opposite Bab al-Hawa.
The last time Turkish forces were engaged in Syria was in August, when Turkey launched its eight-month-long Euphrates Shield operation against jihadists and Kurdish militia in the northern Syrian province of Aleppo. Three other de-escalation zones are now operating in south-western Syria, eastern Ghouta (suburbs of Damascus) and northern Homs province.
Idlib is largely controlled by Hayat Tahrir al-Sham, a group led by Al-Qaeda's former Syria affiliate, which ousted more moderate rebels in recent months.