An explosion in the opposition-held Syrian province of Idlib has killed at least 15 people, rescue workers say.
Three buildings in the town of Jisr al-Shughour were destroyed by the blast, the cause of which was not known.
A monitoring group said it happened in front of an office belonging to the jihadist alliance that largely controls the province, Hayat Tahrir al-Sham.
Idlib has been hit by several bombings in recent months, as well as by Russian air strikes and Syrian army shellfire.
HTS commanders have blamed previous bombings on President Bashar al-Assad's intelligence services and the rival jihadist group Islamic State (IS), saying they are seeking to destabilise the last opposition stronghold remaining in Syria after eight years of civil war which have left more than 370,000 people dead.
Idlib is covered by a six-month-old truce brokered by Russia, which backs Mr Assad, and Turkey, which supports the opposition, that has spared the 2.9 million civilians living there from a government assault and a humanitarian disaster.
A demilitarised buffer zone was established running along the front line to separate opposition and government forces. Mainstream rebels were required to pull their heavy weapons out of the zone, and jihadists were told to withdraw altogether.
But a takeover of the province in January by HTS, which was known as al-Nusra Front until it broke off formal ties with al-Qaeda in 2016, has jeopardised the truce and been followed by an escalation in strikes on opposition-held towns.
Jisr al-Shughour has been subjected to heavy bombardment in recent weeks, and residents said long-range missiles hit several surrounding villages overnight.
Tense moments as #WhiteHelmets work in dangerous conditions to rescue a woman and her husband under slabs of concrete after an unknown explosion hit #Jisr_AlShughour City western #Idlib this morning. 15 people were killed and 30 were injured. #Syria pic.twitter.com/sSdCb1OWmy— The White Helmets (@SyriaCivilDef) April 24, 2019
But the head of civil defence in the town, Ahmed Yaziji, told Reuters news agency that the cause of the explosion on Wednesday morning was not yet known.
The Syrian Observatory for Human Rights, a UK-based monitoring group, said 13 civilians were among those killed. Two were children of members of the Turkistan Islamic Party, a mostly Chinese Uighur jihadist group allied to HTS, it added.
In a separate development on Wednesday, Syrian state media reported that a civilian was killed when a car bomb exploded in the south of the capital, Damascus.