The UN’s chemical weapons watchdog is expected to release its first report explicitly blaming Bashar al-Assad for sarin and chlorine gas attacks on civilians in Syria as efforts to establish accountability for the use of chemical agents in the nine-year-old conflict gain momentum.

Observers anticipate that public and classified versions of a report by a new unit at the Organisation for the Prohibition of Chemical Weapons (OPCW) will be published on Wednesday, close to the anniversaries of a major chlorine attack on the then rebel-held Damascus suburb of Douma that killed at least 85 people in 2018 as well as a deadly sarin attack on Khan Sheikhun in 2017 which killed at least 89. The report is believed to focus on 2017 attacks on the village of al-Lataminah.

The investigation is the outcome of new powers granted to the OPCW by a 2018 UN resolution specifically calling for the watchdog to “put in place arrangements to identify the perpetrators of the use of chemical weapons in the Syrian Arab Republic by identifying and reporting on all information potentially relevant to the origin of those chemical weapons”. Previously, OPCW fact-finding missions did not have the mandate to apportion blame in chemical weapons attacks.

The resulting newly created investigation and identification team (IIT) at the OPCW was designed as a work-around to counter Russia, Syria’s closest political ally. Moscow has repeatedly used international forums - and its veto as a permanent member of the UN security council - to block independent investigations into chemical weapons attacks allegedly launched by the Assad regime.

The IIT report’s expected findings could trigger new sanctions on Syrian officials and are likely to lead to renewed accusations from Moscow, Tehran and Damascus that the OPCW’s work has been politicised by western nations. The charge that Russia permits, or covers up, the regime’s use of chemical weapons on Syrian civilians is one of the most bitter diplomatic flashpoints between Russia and the west.

“Even though the evidence of Assad’s crimes against humanity is incontrovertible, independent fact finding missions have been massively undermined by Russian-led disinformation campaigns,” said Hamish de Bretton-Gordon, chemical weapons expert and director of Doctors Under Fire.

“For example, the supposed whistleblower controversy at the OPCW last year, which the organisation comprehensively rejected with an official inquiry. Even though the criticism was found to be baseless it does not stop the conspiracy theorists.

“If the rules-based global order had actually applied to Syria’s war, then the creation of the IIT would not have been necessary. This [new measure] isn’t perfect but it is a step forward.”

A new dataset and interactive mapping tool, due to be released on Tuesday, gives the most comprehensive analysis of chemical weapons use in Syria to date.

Researchers from the Global Public Policy Institute in Berlin along with Syrian and international partners compiled 345 credibly substantiated or confirmed attacks across the country since 2011, building on what the institute described as years of painstaking research.

Approximately 98% of the attacks were carried out by the Assad regime, usually dropped from the air, and Islamic State are responsible for the rest, GPPI found. Around 90% of the documented attacks were carried out after the infamous “red line” chlorine attack on the Damascus suburb of Ghouta in 2013.

According to the GPPI research, Assad’s heavy use of improvised chlorine bombs, in particular, is a crucial part of the regime’s military strategy: after conventional bombing drives civilians into underground tunnels and basements, chlorine gas, which is heavier than air, sinks into these last refuges, finally forcing people to flee their homes and towns.

“Our research shows what Syrians on the ground have known for years: that chemical weapons have become a completely normalised component of the Syrian regime arsenal used for years in full view of the international community with near impunity,” said Tobias Schneider, a GPPI research fellow who worked on the new resource.

“Syria is commonly described as the ‘best documented war in history’. While that’s true, it is hard to go beyond the individual incident to process and make sense of the vast body of data that the war has produced over the years. We hope this research will inform prosecutions for years to come. But this data has been available for years and could have been used to better inform policymaking that could have averted the worst of these horrors.”