The Turkish military established a third observation point, gaining control over the roads near the Syrian town of Saraqib in the Idlib countryside on Saturday.
Regime forces pushed north from Maarat al-Numan on Thursday toward the town of Saraqib, whose residents have mostly fled in the face of heavy bombardment.
Both Maarat al-Numan and Saraqib lie on the key M5 highway connecting the capital Damascus to the second city Aleppo.
The road has been in the regime's sights as it seeks to revive a moribund economy ravaged by almost nine years of war.
Some 50 kilometers (30 miles) of the M5 remained outside regime control, the Britain-based Observatory said.