Reports from Syria say dozens of people have been treated for breathing problems after a suspected chlorine gas attack in the northern city of Aleppo.
The British-based Syrian Observatory for Human Rights said 70 people suffered from suffocation after a barrel bomb attack in the opposition-held neighborhood of Sukari on September 6.
No deaths were reported.
The Syrian Civil Defense, a volunteer emergency response team that operates in rebel-held areas, said the barrel bombs were dropped by government helicopters and contained chlorine cylinders.
The Civil Defense posted video on its Facebook page showing children using oxygen masks to breathe.
It had accused the government of two suspected chlorine gas attacks last month.
Damascus has denied all accusations it used chemical weapons during the 5-year-old civil war.
A UN-led investigation in August found Syrian government forces were responsible for two toxic gas attacks in 2014 and 2015 involving chlorine.