More than 100 people were wounded in Syria’s Aleppo late on Saturday in a suspected toxic gas attack.
Syria's government and its ally, Russia, blamed the attack on insurgents.
A health official in Aleppo said victims suffered breathing difficulties and eye inflammation suggesting the use of chlorine gas.
Rebel officials denied the allegations and asserted they do not possess chemical weapons.
State news agency SANA said on Sunday 107 people were injured, including children.
A monitoring group said air strikes hit rebel territory in northwest Syria on Sunday.
Russia and Turkey agreed upon a buffer zone in northwestern Syria in September.