A huge explosion ripped through the center of a rebel-held border town in northern Syria on Saturday, killing more than 40 people, many of them civilians displaced by months of conflict that devastated large parts of the nearby city of Aleppo.
Monitors said the blast, most likely from a tanker truck bomb, was detonated in the town of Azaz, outside a courthouse and security offices staffed by opposition fighters seeking to topple the Damascus government. A nearby marketplace lay in ruins.
There was no immediate claim of responsibility.
Video from the scene showed flattened, burning buildings and wounded locals struggling to escape the blast area.
Local activists placed the death toll as high as 60, as search-and-rescue teams scrambled to locate survivors hours after the blast.
Rebel-controlled Azaz has been targeted repeatedly by bombers in recent months, with anti-government militia accusing Islamic State extremists in two bombings in late 2016 that killed more than 40 people, most of them rebels.
The blast coincided with a fragile, nationwide cease-fire brokered in late December by Syrian government ally Russia and Turkey. That truce excluded jihadists from Islamic State and the al-Qaida affiliate Fateh al-Sham, known previously as al-Nusra Front.
In separate developments Saturday, government forces near Damascus pressed forward with an offensive in the Barada Valley aimed at pushing rebels and jihadists from territory that supplies the capital's 5.5 million residents with drinking water.
The activist Syrian Observatory for Human Rights, which monitors fighting in the nearly six-year conflict, said Saturday that at least nine people, including seven government soldiers, had been killed in fighting on the outskirts of Damascus. At least 20 others were reported wounded.
Government forces pounded the area for nearly two weeks, after claims on December 22 that rebels had contaminated the city's water supply. Severe rationing has since crippled daily life in the city and sparked widespread demands from locals for government action to end the crisis.
The government of President Bashar al-Assad has accused rebels of contaminating water from the Barada River with diesel fuel.
But rebel groups dug in at Barada since 2012 linked the contamination to government airstrikes in December that they say heavily damaged a key water-processing facility that supplies the city.