At least 17 people were killed on Wednesday in an explosion in the centre of Jisr al Shughour, a rebel-held city in northwestern Syria, a day after heavy Russian air strikes in the vicinity, rescue workers and residents said.
Several residential buildings collapsed as a result of the blast in Idlib province, near a road between the coastal city of Latakia and city of Aleppo.
“The casualties are expected to rise. The cause is not known,” said Ahmad Yaziji, head of civil defense in the city, adding at least 27 people, mostly civilians, were injured.
Bodies were still being pulled out of the rubble, another rescuer said.
The province and areas around it in northern Syria, the last remaining rebel bastion, have seen an escalation in attacks by Russian warplanes and the Syrian army even though they are protected by a “de-escalation zone” agreement brokered last year between Russia, Iran and Turkey.
The bombardment has sent people fleeing from opposition-held towns in the buffer zone that straddles parts of Idlib to northern Hama and parts of Latakia province.
Turkey, which has supported the rebels and has troops to monitor the truce, has been negotiating with Moscow to halt the Russian strikes with little success.
Russian jets hovered in the sky with missile strikes reported in several villages around Jisr al Shughour, residents said.
Overnight, Russian jets struck western parts of Idlib city and residents said long-range missiles hit several villages surrounding Jisr al Shugour from army positions in Latakia
Jisr al Shughour has been a target of heavy bombardment by the Russian air force and the Syrian army in recent weeks. Most of its inhabitants have fled to the safety of areas close to the Turkish border, residents and local officials say.
The Idlib region is under administrative control of Hayat Tahrir al-Sham, Syria's former Al-Qaeda affiliate.
But the Turkestan Islamic Party, a group of foreign extremists from the ethnic Uighur Muslim minority, also has a large presence in Jisr al-Shughur.
The ISIS extremist group has sleeper cells in the wider Idlib region.
Idlib has since September been protected from a massive regime offensive by a fragile ceasefire deal signed by Damascus ally Russia and rebel backer Turkey.
But the region of some three million people has come under increasing bombardment since HTS took full control of it in January.
On Tuesday, regime shelling killed seven civilians, including four children, in the town of Khan Sheikhun.
Increased regime shelling on Khan Sheikhun has sparked one of the largest waves of displacement since the September deal.
Syria's war has killed more than 370,000 people and displaced millions since the conflict began with the repression of anti-government protests in 2011.