The latest alleged use of chemical weapons on Syria's civilian population came last Tuesday, with footage of an apparent chlorine gas attack on the Sukri neighbourhood in Aleppo showing crying children being doused with water and then lying on hospital beds and breathing through respirators.

The Syrian Civil Defence, a rescue workers' group that operates in rebel-held areas, said government helicopters dropped barrel bombs containing chlorine that caused suffocation in 80 people. By Wednesday, the Syrian Observatory For Human Rights said that one person had died as a result of the attack. The Syrian army denied the accusations.

Syria's chemical weapons attacks are likely to come to the fore this month when the United Nations Security Council meets to discuss that country. During a closed-door session at the end of August, the council failed to agree on sanctions or other actions when presented with findings by a UN team that Syrian government forces twice used chemical weapons in the civil war.

Story continues below advertisement

A year-long joint investigation by the UN and Organization for the Prohibition of Chemical Weapons focused on nine attacks in seven areas of Syria. A separate OPCW fact-finding investigation had found chlorine has been "systematically and repeatedly" used as a weapon during the Syrian conflict. Government and opposition forces have denied using chlorine.

But when the council met to discuss the report in August, Russia questioned the evidence from the independent commission, though the country did support the establishment of the OPCW-UN Joint Investigative Mechanism, charged with determining who was responsible for the attacks and paving the way for possible punishment.

Investigators are expected to prepare one more report before the group's mandate ends on Sept. 23, which will give more details on three attacks (Nos. 2, 7 and 8 on the map). Eight of the attacks investigated involved the use of chlorine. The inquiry was unable to reach a conclusion in six cases.

Virginia Gamba, who headed the inspection team, defended the group's methodology but conceded that it was difficult to prove the use of chlorine, which is commercially available and evaporates quickly.

Because of her team's narrow mandate, she said inspectors only scratched the surface of chemical weapons use in Syria, adding that they were "acutely aware of the ongoing use of chemicals as weapons in the Syrian Arab Republic."

Chlorine's use as a weapon is prohibited under the 1997 Chemical Weapons Convention, which Syria joined in 2013. If inhaled, chlorine gas turns to hydrochloric acid in the lungs and can kill by burning lungs and drowning victims in the resulting body fluids.

1. Kafr Zita in Hama governorate on April 11, 2014. The inquiry did not recommend further investigation.

Story continues below advertisement

2. Attacks in Kafr Zita on April 18, 2014, merit further investigation. Findings are expected in coming weeks.

3. Al-Tamanah on April 29-30, 2014. The inquiry did not recommend further investigation.

4.Al-Tamanah on May 25-26, 2014. The inquiry did not recommend further investigation.

5. The inquiry found the Syrian Arab Air Force helicopters dropped devices, potentially barrel bombs, that released toxic substances including chlorine on Talmenes, in Idlib governorate, on April 21, 2014.

6. Syrian Arab Air Force helicopters dropped devices "consistent with the construction of a barrel bomb" that released toxic substances, including chlorine, on Sarmin, in Idlib governorate, on March 16, 2015. Barrel bombs are steel drums full of shrapnel and explosives dropped from the air.

7. Attacks on Qmenas, in Idlib governorate, on March 16, 2015, merit further investigation. Findings are expected in coming weeks.

Story continues below advertisement

8. Attacks on Binnish in Idlib governorate on March 24, 2015, merit further investigation. Findings are expected in coming weeks.

9. Islamic State militants were the "only entity with the ability, capability, motive and the means to use sulphur mustard gas" in an attack on Marea on Aug. 21, 2015.

Staff, with reports from wire services