The Syrian government used banned chemical weapons against opposition forces in 2018 in the city of Douma, the Organization for the Prohibition of Chemical Weapons (OPCW) said on Friday.

The watchdog noted that there were "reasonable grounds to believe that the Syrian Arab Air Forces were the perpetrators."

In a new report, the organization said at least one helicopter of Syria's air forces dropped two yellow cylinders, containing toxic chlorine gas, on residential apartment buildings in Douma, killing 43 people and affecting dozens more in 2018.

Director-General Fernando Arias said that "the use of chemical weapons in Douma — and anywhere — is unacceptable and a breach of international law."

Syria's foreign ministry responded on Saturday by saying that the OPCW report lacked any evidence and denying the allegations made against Bashar Assad's regime.

"Syria totally rejects the report," the foreign ministry said in a statement carried by state news agency SANA. It also said that the document "lacks scientific proof" and reached "false conclusions." 

Multiple chemical attacks in Syria

OPCW investigators are not tasked with assigning criminal responsibility, the organization said on its website.

However, their conclusions are reached "on the basis of 'reasonable grounds,' which is the standard of proof consistently adopted by international fact-finding bodies and commissions of inquiry," according to the OPCW.

Syrian President Bashar Assad and his forces have been repeatedly accused of using chemical weapons during the country's civil war, which is now in its twelfth year.

As of December 2022, investigators from the United Nations and OPCW have found at least eight instances where chemical weapons were used by Syrian central government forces. The OPCW is responsible for enforcing the ban on chemical weapons globally.

What happened in Douma?

Douma is part of the suburb of Ghouta approximately 10 kilometers (6.2 miles) northeast of the capital Damascus. Eastern Ghouta became one of the first areas to join the uprising against Syria's central government in 2011.

Threatened by opposition forces near its capital, the Syrian central government cut off water supplies and electricity to Ghouta, later encircling the area in 2013 and launching one of the longest running sieges in modern times.

The enclave witnessed some of the worst atrocities of the Syrian war between 2013 and 2018.

What to know about chemical attacks in Syria

Investigators from the OPCW blamed three chemical attacks in 2017 on Assad's government in April 2020. In 2021, the international chemical weapons watchdog blamed yet another chemical weapons attack on a northern Syrian town in 2018 on Assad's forces as well.

Following the reports, the organization stripped Syria's membership rights within the body in 2021 — marking the first time the OPCW had issued such sanctions against a member nation.

Syrian claims of having destroyed chemical weapons in doubt

Syria joined the Chemical Weapons Convention (CWC) in 2013, after being pressed into destroying its chemical weapons stock following an attack on rebel forces using sarin gas in Ghouta.

By August 2014, the Assad government declared the destruction of its lethal stockpile was completed. But Syria's initial declaration of its chemical stockpiles remains in dispute.

Russia, one of Syria's strongest allies, has also repeatedly blocked actions at the UN Security Council to punish Assad.

Edited by: Darko Janjevic