BEIRUT (AP) — The Latest on the Syrian conflict (all times local):

4:30 p.m.

Syrian opposition activists say a mysterious blast in the country's north has killed at least 36 people, including children.

The opposition-run Syrian Civil Defense, first responders also known as the White Helmets, said Sunday's blast occurred in the village of Sarmada near the Turkish border, killing 36 people and wounding many others.

It says the explosion collapsed two five-story buildings, burying many of the victims.

The Britain-based Syrian Observatory for Human Rights put the death toll at 39, including 21 women and children.

The Observatory says an arms depot in the basement of a building exploded. It says the depot was run by an arms dealer close to the Levant Liberation Committee, an al-Qaida-linked group.

The Observatory says many of the residents killed were displaced earlier this year from the central province of Homs.

12:30 p.m.

Syrian opposition activists say an explosion in the country's north has killed at least 18 people and wounded many others. The cause of the blast wasn't immediately known.

The opposition-run Syrian Civil Defense, also known as White Helmets, says the blast occurred Sunday in the village of Sarmada near the Turkish border and "killed and wounded dozens." The explosion collapsed a five-story building, burying many of the victims.

The Britain-based Syrian Observatory for Human Rights put the death toll at 18. It's unclear if the casualties are all civilians.

The Observatory says an arms depot in the basement of a building had detonated. It says the depot was run by an arms dealer close to the al-Qaida-linked Levant Liberation Committee.

Meanwhile, Syrian government forces are fighting rebels in Idlib province.