Syrian rebels sit on the front line facing regime areas in the southern countryside of Aleppo on Sunday. (Omar Haj Kadour/AFP/Getty Images)

Militants in Syria indicated tepid support for a demilitarized zone in the country’s final opposition stronghold, even as they appeared to defy an internationally brokered deadline Monday for their withdrawal. 

The area surrounding the northern province of Idlib is home to about 2.5 million people, most of them civilians. Aid groups have warned that an offensive there could spell a humanitarian catastrophe. 

A Sept. 17 deal between Russia and Turkey — key backers of Syria’s government and rebel forces, respectively — called for heavy weapons and Islamist militant groups to be pulled out of a roughly 13-mile-wide buffer zone.

But as the deadline passed, monitoring groups said that although a bloc of Turkey-backed rebels had withdrawn their weapons, the province’s most extreme militants were still there. 

“We value the efforts of all those striving — at home and abroad — to protect the liberated area and prevent its invasion and the perpetration of massacres in it,” the al-Qaeda-linked Hayat Tahrir al-Sham, or HTS, said in a statement late Sunday. 

“But we warn at the same time against the trickery of the Russian occupier or having faith in its intentions,” it added. The militant group also said it “would not forget” the foreign fighters who came to assist it.

Analysts interpreted the statement as a sign that HTS — whose reluctance to withdraw could present one of the biggest obstacles to the deal — would grudgingly comply. 

“HTS’s statement seems to amount to a tacit acceptance of the [agreement’s] terms, even as HTS rejects more far-reaching concessions like renouncing armed struggle and voices its distrust of the deal’s Russian co-sponsor,” said Sam Heller, senior analyst on nonstate armed groups for the International Crisis Group. 

The stakes are high. President Bashar al-Assad’s government routinely emphasizes its desire to control every inch of Syria, nearly seven years into a war that tore more than a third of the country from its grasp. 

In the event that the Turkey-Russia deal breaks down, the Syrian military could still launch a grinding offensive to uproot extremists from Idlib.

“Over and over again, similar deals have simply ended in a bloodbath,” Wouter Schaap, Syria country director for the Care International aid organization, said last week. “Civilians caught in this standoff must be spared at all costs.”

Russian officials have indicated that they view the deadline as flexible, with the militants’ failure to withdraw unlikely to meet with immediate violence. “The quality of that work is far more important. We strongly support our Turkish partners’ efforts,” Russian Foreign Minister Sergei Lavrov said Wednesday. 

Heller said the deal’s success hinges on Russia’s flexibility and willingness to support Turkey as the latter works out the kinks of implementation.

Both have a vested interest in keeping the peace. In Ankara, the risk is that an all-out offensive could send refugees pouring into Turkey. Russia is trying to disentangle itself from a war on which it has spent billions of dollars. 

The skies over Idlib and slivers of the neighboring Aleppo and Latakia provinces have fallen largely silent since Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan announced last month that their proxies would respect a cease-fire.

After weeks in which a major offensive had seemed inevitable, civilians across the opposition-held pocket have voiced relief, and even optimism, at the improvement in living conditions that accompanied the pause in fighting. 

“Celebration halls are now open and always busy with weddings and other ceremonies. People have basically returned to normal life,” said one doctor, speaking on the condition of anonymity because of concerns for his safety.

But aid groups warned that the break in fighting had yielded few meaningful changes in the humanitarian situation. “Aid workers across the network of camps are telling us that up to 45 percent of school-age children are out of formal education, going to makeshift classes in shanty tents,” said Rachel Sider, advocacy and information adviser on Syria for the Norwegian Refugee Council.

Local doctors and humanitarian workers also say they have been subjected to a growing campaign of arrests, kidnappings and intimidation by extremist groups.

With Syria’s rebel forces nearing defeat, Assad’s government is renewing trade ties with neighbors. 

As the United Nations oversaw a ceremony Monday to mark the reopening of a crossing between Syria and the Israeli-occupied Golan Heights, Syrian officials announced that a key outpost on the Jordanian border, Naseeb, was open for business. Both had closed during the war as opposition fighters took up positions nearby.

The reopening of major highways and trade routes has emerged as a priority for Syrian authorities as the fighting ebbs, and the state signals to its citizens and the world that the country is back in business. 

Iraqi Foreign Minister Ibrahim al-Jafari arrived in Damascus on Sunday for talks to hasten the opening of a crossing along the shared border. “My visit to Syria is significant, as I sensed the stability and security after its victory over terrorism,” Jafari said, according to Syrian state media.