AMMAN (Reuters) - Syrian rebels said on Thursday they have growing confidence that their jihadist rivals will comply with a requirement to leave a demilitarized buffer zone set up by Turkey and Russia to avert a Russian-backed Syrian army offensive.

Last week Turkey and Russia agreed to enforce a new demilitarized zone in Idlib province from which “radical” rebels will be required to withdraw by the middle of next month.

The position of the biggest jihadist group, Tahrir al-Sham, spearheaded by al Qaeda’s former Syrian offshoot, will be crucial to the deal’s success, but it has so far said nothing.

Several rebel sources said neither jihadist nor mainstream rebels had started to pull back yet.

However, a senior Syrian opposition official said Tahrir al-Sham had sent secret feelers to the Turkish army though third parties in recent days signaling it would comply.

“Matters are moving well and Tahrir al-Sham has pledged it is going to implement but without announcing its agreement,” said the opposition official, who was briefed by Turkish officials and requested anonymity due to the sensitivity of the matter.

The demilitarized zone will be 15 to 20 km (10 to 12 miles) deep, run along the contact line between rebel and government fighters, and will be patrolled by Turkish and Russian forces. The agreement could unravel quickly if they cannot impose their plan on the jihadists.

Another senior opposition figure said he expected Tahrir al-Sham to implement the deal and dismissed risks of a showdown because the agreement did not seek to force jihadist fighters to hand over their weapons.

“I foresee it will be implemented within the time set,” said Ahmed Toma, a prominent opposition figure who headed the Syrian rebel delegation in Russian-sponsored talks in the Kazakh capital.

Turkey sought to avert the Syrian army’s Idlib offensive, fearing a new exodus of refugees as the U.N. warned of a humanitarian catastrophe. Ankara pledged to Moscow it would handle the jihadist threat.

A regional intelligence source said the jihadists were softening their stance to avoid internecine fighting with mainstream rebels that could wreck the deal and allow the stalled offensive to resume.

“I don’t expect any hurdles in implementation from all the revolutionary forces at all,” said Abdul Salam Abdul Razzak, a leading figure in the National Front for Liberation, the alliance of Turkey-allied Free Syrian Army (FSA) rebel groups.

Turkish President Tayyip Erdogan said in an interview with Reuters late on Tuesday that the withdrawal of “radical groups” had already started.

Another senior rebel source said months of covert Turkish intelligence efforts were focusing on separating a minority of foreign jihadists within Tahrir al-Sham from a majority of its Syrian followers, who could eventually be rehabilitated.

Precision strikes would help to handle foreign jihadists, whose presence has often been cited by the Syrian army and Russia as the reason for an assault on Idlib as a “terrorist nest”, the source said.

The National Front for Liberation, which had declared its “complete cooperation” with the Turkish effort, said it foresaw a smooth operation once logistical preparations with Turkey were concluded.

“Pulling heavy arms from the frontline is not a difficult matter as most of these weapons are deployed away from the frontline,” Abdul Razzak said, adding the group’s only concern was whether the Syrian army and its allies would abide by the deal.