WATCH: Amateur video published online appears to show the first moments of a car bomb explosion in the Syrian border town of Azaz, north of Aleppo.
Activists and rescue workers say at least 43 people were killed after a car bomb went off in a busy market in the town of Azaz on Saturday.
The explosion took place in the central market of the rebel-held Syrian town along the Turkish border, damaging a government building and local court house.
Rami Abdurrahman, the head of the Syrian Observatory for Human Rights monitoring group, says a rigged water or fuel tanker was the cause of the explosion, which explains the large blast and high death toll.
He added that six opposition fighters are among those killed.
The Azaz Media centre and other activist groups have put the death toll at 50 following search and rescue operations that continued for at least two hours after the explosion.
According to media activist Baha al-Halabi, witnesses say many bodies were unidentified due to the strength of the explosion.
Many rebels and civilians settled in Azaz after they were pushed out of Aleppo during a massive government offensive late last year.
To the west of the city, Syrian Kurdish forces attempt to advance toward the town, which has caused friction with Turkish troops and allied Syrian opposition fighters.
In the east, opposition fighters backed by Turkey are advancing on the IS-stronghold town of al-Bab.
There has been no immediate claim of responsibility.