Updated

Syria's opposition activists and rescue workers say at least 15 people were killed when a car bomb went off in a busy market in a Syrian rebel-held town along the Turkish border.

The Syrian Civil Defense, a team of first responders, says the initial casualty count shows that at least 15 people died Saturday in the explosion in Azaz, a border town in the northern province of Aleppo. The Syrian Observatory for Human Rights monitoring group put the death toll at 19, and other activists said the number is likely higher after the explosion ripped through a busy market.

Many rebels and civilians who were pushed out of Aleppo city during a massive government offensive late last year resettled in Azaz.

There was no immediate claim of responsibility.