Syrian government and Russian planes have targeted the southern edge of Idlib province with a series of air strikes, activists said.
The strikes have ratcheted up the pressure on the densely populated rebel-held bastion, a day after Iran and Russia backed a military campaign in the area despite Turkey’s pleas for a ceasefire.
Turkey has troops and observations points that ring Idlib.
The Britain-based Syrian Observatory for Human Rights reported more than 30 air raids on Saturday on a number of towns and villages in south-western Idlib and adjacent northern Hama province, an area targeted over the last few days which overlooks government-controlled areas.
Schools were shut in Khan Sheikhoun, an area under attack, because of the raids, the Observatory reported.
State-run Al-Ikhbariya TV said the government was retaliating against overnight shelling from rebel-held areas on a government-held town in Hama province, south of Idlib.
The shelling late on Friday in Mhradah killed nine civilians, according to state media.
The local council of Morek, a town that serves as a crossing between Hama and Idlib, sent an urgent appeal, asking Turkey for a quick solution.
Separately, clashes broke out in eastern Syria in Qamishli, a town close to the border with Turkey, between government and Kurdish security members.
The Observatory said the clashes left 10 government security personnel and seven Kurdish fighters dead.
The town is run by Kurdish-led administrators and forces, but Syrian government troops hold pockets of territory there, including the airport.
Clashes rarely erupt there over turf control and authority, and are usually a reflection of deepening political tension between uneasy partners.