OPCW report found that at least one Syrian air force helicopter dropped toxic gas on the rebel-held town of Douma.

Syria’s foreign ministry said on Saturday that a report by the Organisation for the Prohibition of Chemical Weapons (OPCW) that found the Syrian government was responsible for a chlorine attack on the rebel-held Syrian city of Douma lacked any evidence.

“Syria totally rejects the report”, the foreign ministry said in a statement carried by state news agency SANA.

“The report lacks scientific proof,” it said, decrying “false conclusions”.

In the OPCW report, investigators said there were “reasonable grounds to believe” that at least one Syrian air force helicopter had dropped two cylinders of the toxic gas on the rebel-held town of Douma.

Weaponising chlorine is prohibited under the Chemical Weapons Convention and international humanitarian law.

Damascus and its ally Moscow have said the April 7, 2018 attack was staged by rescue workers at the behest of the United States, which afterwards launched air raids on Syria along with the United Kingdom and France.

The OPCW dismissed claims that rebels and emergency workers had staged the attack.

Its team “thoroughly pursued lines of inquiry and scenarios suggested by Syrian authorities and other state parties, but was unable to obtain any concrete information supporting them”.

Emergency workers said at the time that they had treated people suffering from breathing problems, foaming at the mouth and other symptoms.

Survivors and activists described to Al Jazeera in 2018 how they struggled to breathe and continued to suffer effects after the attack.

The Douma case caused controversy after leaks from two former employees accused the Hague-based watchdog of altering its original findings to make them sound more convincing.

But the OPCW said its investigators had “considered a range of possible scenarios” and concluded that “the Syrian Arab Air Forces are the perpetrators of this attack.”

Damascus has denied the use of chemical weapons and insisted it has handed over its stockpiles under a 2013 agreement, prompted by a suspected sarin gas attack that killed 1,400 in the Damascus suburb of Ghouta.

Syria’s voting rights at the OPCW were suspended in 2021 for its refusal to cooperate after being accused of more chemical attacks.

Nearly half a million people have been killed in Syria’s conflict, which began in 2011 and has displaced about half of the country’s pre-war population.