Updated

Syrian activists, rescuers and medics say a poison gas attack on a rebel-held town near the capital has killed at least 40 people.

The alleged attack in the town of Douma occurred Saturday night amid a resumed offensive by Syrian government forces after the collapse of a truce.

The Syrian Observatory for Human Rights said at least 80 people were killed in Douma Saturday, including around 40 who died from suffocation.

Opposition-linked first responders, known as the White Helmets, also reported the attack, saying entire families were found suffocated in their houses and shelters. It reported a death toll from suffocation of more than 40.

The Syrian American Medical Society, a relief organization, says 41 people were killed and hundreds wounded.