At least 27 people, including three children, were killed Monday when a car bomb exploded in the town of Darkush in northwestern Syria, near the Turkish border, an NGO said.
The Syrian Observatory for Human Rights, which had earlier reported a toll of 20, said the number of casualties was expected to rise due to the large number of people who suffered serious injuries.
"The toll has risen to 27 dead, including three children and a woman, as a result of a car bomb blast," said the Britain-based Observatory, which relies on activists across the country for its reports.
Activists from the Syrian Revolution General Commission network said the blast took place in the market area of Darkush, which is under rebel control. The Observatory confirmed the report.
A video posted online by activists showed the aftermath of the blast, with at least one car ablaze and the ground around it covered with smoking embers.
A second video showed residents carrying bodies on makeshift stretchers and extensive damage to buildings around the blast site.
Darkush, which lies on the Orontes river, is just a few kilometres (miles) from the border with Turkey.
The Syrian opposition National Coalition condemned the "terrorist bombing" in a statement, noting that it came a day before Muslims mark the beginning of the Eid al-Adha religious holiday.
"The Coalition points the finger at the regime of (Syrian President) Bashar al-Assad, which is trying to create confusion and chaos and provoke tensions in the ranks of the rebels, as well as take revenge against civilians for defeats of the army," the Coalition said.