On Jan. 2, Hayat Tahrir al-Sham captured Darat Izza and four other towns in western Aleppo and the National Liberation Front's Nour al-din al-Zenki fighters took refuge in Turkey-controlled Afrin, leaving behind dozens of vehicles, including tanks. The National Liberation Front retaliated by taking three localities in southern Idlib from Hayat Tahrir al-Sham.

The clashes erupted Jan. 1 after the National Liberation Front's Nour al-din al-Zenki Movement killed five Hayat Tahrir al-Sham fighters in Darat Izza, drawing in other National Liberation Front groups such as Ahrar al-Sham, Thuwar al-Sham and Biyareq al-Islam. For the National Liberation Front factions, the outcome was a debacle. In 10 days, they lost nearly 90 localities to Hayat Tahrir al-Sham, greatly complicating the September deal Turkey and Russia had reached in Sochi to establish the de-escalation zone around Idlib in areas including parts of western Aleppo, northwestern Hama and northeastern Latakia.

Since the beginning of January, Hayat Tahrir al-Sham — a coalition of Islamist factions in northern Syria — has routed the opposition groups Turkey had merged under the banner of the National Liberation Front .

As Turkey faces obstacles in the Syrian military operation it plans for Manbij and northeast Syria, drama is developing in Idlib province, where 12 Turkish posts overlook what is supposed to be a de-escalation zone.

On Jan. 3, while clashes continued elsewhere, Hayat Tahrir al-Sham seized four localities in Hama province. The following day, Hayat Tahrir al-Sham also made advances also in western Aleppo, capturing Sinhar, al-Hutah and the military base in Sheikh Suleiman that had been Nour al-din al-Zenki’s main headquarters.

On Jan. 6, Thuwar al-Sham and Biyareq al-Islam raised a white flag in Al-Atarib. Some 1,000 fighters from those two factions left the city under a deal.

On Jan. 9, Ahrar al-Sham handed over al-Ghab Plain and Shashabo Hill in Hama governorate to Hayat Tahrir al-Sham, which required Ahrar al-Sham to disband in those two regions.

In sum, all factions in southwestern Idlib province surrendered their ground to Hayat Tahrir al-Sham, except for Jaysh al-Izza, which didn't take part in the clashes. In southern Idlib alone, Hayat Tahrir al-Sham took control of 33 localities.

Another critical development involved the Aleppo-Hama-Homs-Damascus road (M-5) and the Aleppo-Latakia road (M-4). Hayat Tahrir al-Sham increased its control on both routes, bringing to 80% the area controlled by Hayat Tahrir al-Sham and like-minded jihadi groups.

Hayat Tahrir al-Sham also besieged Ariha and Maarat al-Numan, but, facing protests from the local population, didn't enter the towns immediately.

On the 10th day of the clashes, Hayat Tahrir al-Sham and the National Liberation Front signed a cease-fire deal that requires them to remove road barricades and checkpoints and mutually release captives. The so-called Salvation Government, the civilian arm of Hayat Tahrir al-Sham, will take over administration of all areas Hayat Tahrir al-Sham captured in those 10 days, along with Ariha and Maarat al-Numan. However, similar agreements signed in the past quickly collapsed. Should this deal collapse as well, Hayat Tahrir al-Sham could advance even farther if Turkey doesn't intervene — which it hasn't, so far.

Turkey is, however, reinforcing its border, sending commandos and armored vehicles to its Hatay province on the border with Idlib, Turkey's state-run Anadolu Agency news group reported Jan. 11.

The Syrian border abutting Turkey is now completely in Hayat Tahrir al-Sham hands. Hayat Tahrir al-Sham has surrounded most of the observation points that the Turkish military set up around Idlib under the Sochi deal. The National Liberation Front has proved a disappointment.

Hayat Tahrir al-Sham's advances defied expectations that the group would weaken further under the impact of the Sochi deal, on top of its loss of thousands of fighters following the defection of Nour al-din al-Zenki and other groups. The Sochi agreement required Hayat Tahrir al-Sham fighters to pull out of the buffer zone encircling Idlib. Turkish security sources told the BBC in November that the number of Hayat Tahrir al-Sham fighters in Idlib had fallen to about 12,000 from its peak of more than 17,000.

Turkey hoped it could move the Sochi deal forward as a result of proxy operations without involving its own troops, through subtle interventions by its intelligence service and by negotiation. But the buffer zone, which was supposed to be cleared of terrorist groups and heavy weaponry, has fallen largely into Hayat Tahrir al-Sham's hands. Another Sochi commitment required the reopening of the M-5 and M-4 roads by the end of 2018. To keep its word, Turkey should now intervene, or acquiesce to the big offensive that Russia and Syria had put off.

Ankara watched in silence as Hayat Tahrir al-Sham advanced in recent days, giving rise to certain suspicions. Observers ask why Turkey didn't help the National Liberation Front, a question that brings along a second one: Could it be that Turkey has made some deal with Russia?

One potential scenario is that Turkey might have forfeited Idlib in return for Manbij. According to another scenario, Turkey could let Russia go ahead rather than keep its end of the bargain in the Sochi deal and draw the wrath of jihadis upon itself. Although such a deal with Russia can't be ruled out, eschewing intervention is not really out of sync with Turkey’s general strategy in Syria in years past.

In 2014, Turkey refrained from directly intervening even in the clashes between its ally, the Free Syrian Army, and the Islamic State, which had reached Turkey’s borders. Instead, it chose to beef up support for its allies to tip the scales. It stuck to the same tactic later, when the factions of the Army of Conquest began to fight each other after taking hold of Idlib.

An important difference today is that Turkey is on the ground with 12 observation posts, which has raised expectations. Still, Turkey never considered confronting Hayat Tahrir al-Sham militarily, despite the commitments Ankara made. Rather, it counted on its persuasion and deterrence abilities to fix things on the ground. In return, Hayat Tahrir al-Sham — which relies on the Turkish borders for supplies — gave the nod to Turkey’s observation posts and even escorted Turkish troops on the ground. This, however, doesn't mean Hayat Tahrir al-Sham will acquiesce to Turkey's swaying the battlefield in coordination with Russia or mobilizing rebel groups against the Kurds.

A Hayat Tahrir al-Sham sheikh, for instance, has criticized groups willing to join Turkey’s planned operation east of the Euphrates against the Kurdish People’s Protection Units (YPG), arguing that involvement in “a war between a secular army and an atheist party” is incompatible with Islam.

A spokesman for the National Army, another Turkish-backed rebel force, has accused the jihadis of attempting to distract Turkey-allied forces to keep them from participating in Turkey's plans to attack the YPG and seize Manbij and towns on the eastern bank of the Euphrates. (That operation became complicated, however, when Syria sent military forces to fortify Manbij at the Kurds' request.) It is a fact, however, that the latest jihadi clashes were fanned by attacks by Ahrar al-Sham and Nour al-din al-Zenki on Hayat Tahrir al-Sham. As early as Dec. 3, Hayat Tahrir al-Sham reported deadly fighting with Ahrar al-Sham after the latter attempted to seize Hayat Tahrir al-Sham territories while the Syrian army fortified positions to the south.

Finally, regardless of whether a secret plan is at play in the background, the latest developments have led to a situation in which Turkey can no longer shield the “jihadi reserve” of Idlib.