The so-called Syrian Observatory for Human Rights (SOHR) said on Sunday that the Turkey-backed Failaq al-Sham militant outfit was the first to abide by the terms of the Moscow-Ankara agreement on the Idlib demilitarized zone.
"The group is withdrawing its forces and heavy arms in small batches from southern Aleppo countryside, adjacent to Idlib Province, which is part of the demilitarized zone towards the west," SOHR head Rami Abdulrahman said.
Earlier this month, Turkish President Recep Tayyib Erdogan and his Russian counterpart, Vladimir Putin, met in the Black Sea resort of Sochi and announced an agreement on Idlib.
The deal stipulates a demilitarized zone of 15-20 kilometers in Idlib along the contact line between the armed opposition and Syrian government troops by October 15. It also involves the withdrawal of “radically-minded” militants, including the al-Nusra Front, from the region.
Under the Idlib agreement, Turkey and Russia would carry out coordinated military patrols on the borders of the buffer zone in a bid to detect and prevent "provocation by third parties."
A US-backed militant group however on Saturday rejected the deal in Idlib, the last major terrorist bastion in the Arab country.
The Jaysh al-Izza faction, affiliated with the Turkish-backed so-called Free Syrian Army, said the Idlib demilitarized zone would only encompass territory currently controlled by anti-Damascus militants.
The buffer zone, it added, should be carved out equally from both terrorist-held areas and nearby regions under the control of Syrian government forces.
"We are against this deal, which eats into liberated (occupied) areas and bails out [Syrian President] Bashar al-Assad," Jaysh al-Izza head Jamil al-Saleh told AFP.
With an estimated 2,500 members, the Jaysh al-Izza militant outfit is mainly operating in Syria's west-central Hama Province, bordering Idlib.
The group, which has been supplied with anti-tank missiles by the US, refused to join the so-called National Liberation Front (NLF), a recently formed alliance of militant factions supported by Ankara.
Last week, the NLF rejected laying down its arms or surrendering the territory under its control in Idlib.
Hayat Tahrir al-Sham has yet to state its position on Idlib deal but on Thursday, a senior militant official told Reuters that the militant outfit had sent secret feelers to the Turkish army signaling they would comply with the buffer zone agreement.
Over the past few months, Syrian forces have made sweeping gains against Takfiri elements, especially in the country's southern areas and Damascus suburbs.
Now, the Syrian army is preparing for peacefully ridding Idlib from several foreign-sponsored terrorist groups.