Syria conflict: Government helicopters 'drop chlorine' on Aleppo
Syrian government forces have been accused of dropping barrel bombs containing chlorine from helicopters on a suburb of Aleppo, injuring 80 people.
Volunteer emergency workers say people suffered breathing difficulties after an attack on the Sukkari area.
The reports could not be independently verified. A UN-led inquiry concluded last month that the government had used chlorine on at least two occasions.
The Syrian government has always denied using chemical weapons.
It comes as Syrian opposition leaders prepare to meet in London on Wednesday to launch a new plan for a political transition to try to end the five-year civil war.
The umbrella group representing opposition factions, the High Negotiations Committee, will be hosted by UK Foreign Secretary Boris Johnson.
Foreign ministers from the Friends of Syria group of countries, which have supported the rebellion against President Bashar al-Assad, will also attend.
Saudi Foreign Minister Adel al-Jubeir told the BBC that he still believed in a political solution to the conflict, and that Mr Assad was not in a "position of advantage or victory", despite his forces' recent advances.