Air strikes on the largely opposition and rebel-controlled region of northern Idlib followed air raids on Tuesday night and Wednesday that killed 23 civilians.
Syrian regime aircraft bombed several towns in north-western Syria on Thursday, killing five civilians as troops and militia battled rebels and opposition fighters on the ground, a war monitor said.
Bombardment of the largely rebel-controlled region of Idlib followed strikes on Tuesday night and Wednesday that killed 23 civilians, 12 of them at a busy market.
In neighbouring Hama province, Syrian troops battled for a third straight day to repel a rebel counterattack around the town of Kafr Nabuda, leaving 15 combatants dead, 11 of them rebels, the Syrian Observatory for Human Rights said.
Syrian regime forces retook the town on May 8, but the rebels retook most of it on Wednesday, the Britain-based monitor said.
More than 100 combatants have been killed in the fighting around Kafr Nabuda since Tuesday.
The Hayat Tahrir al Sham alliance, which is led by Al Qaeda's former Syria affiliate, controls much of Idlib as well as adjacent slivers of Aleppo, Hama and Latakia provinces.
Attack on Hmeymim Air Base
Also on Thursday, militants fired four rockets towards Russia's Hmeymim Air Base in Syria, but all the rockets were destroyed, RIA news agency cited Russia's defence ministry.
Syrian regime officer Mohammad Zuhair Kharboutly said on Thursday that Al Zara power station, close to the rebels' last stronghold in the country's northwest, has been repaired after insurgents bombed the facility the night before, kicking it offline.
The region is nominally protected by a buffer zone deal, but the regime and its ally Russia have escalated their bombardment in recent weeks, seizing several towns on its southern flank.
The UN has warned that an all-out offensive on Idlib region would lead to a humanitarian catastrophe for its nearly three million residents.
More than 200,000 people have already been displaced by the upsurge of violence since April 28, the UN has said.
A total of 20 health facilities have been hit by the escalation – 19 of which remain out of service, it added.