Nearly 40 people, including twelve children, are reported to have been killed in an explosion in a residential building in Syria's rebel-held city of Idlib.
The Syrian Observatory for Human Rights said the building contained weapons and ammunition belonging to an arms trafficker.
Dozens of people remain missing and a search and rescue operation is underway.
The monitor said the previous death toll of twelve climbed after more bodies were retrieved from the rubble.
The cause of Sunday's explosion is not yet clear.
Idlib is Syria's last major rebel-held area and is expected to the next target for the country's military.