Syria agreed in 2013 to join the Organisation for the Prohibition of Chemical Weapons, shortly after an alleged chemical gas attack killed more than 1,400 people near Damascus.

"Despite more than a decade of intensive work, the Syrian Arab Republic chemical weapons dossier still cannot be closed," the watchdog's director-general Fernando Arias told delegates at the OPCW's annual meeting.

The Hague-based global watchdog has previously accused President Bashar al-Assad's regime of continued attacks on civilians with chemical weapons during the Middle Eastern country's brutal civil war.

"Since 2014, the (OPCW) Secretariat has reported a total of 26 outstanding issues of which seven have been fulfilled," in relation to chemical weapon stockpiles in Syria, Arias said.

"The substance of the remaining 19 outstanding issues is of serious concern as it involves large quantities of potentially undeclared or unverified chemical warfare agents and chemical munitions," he told delegates.

Syria's OPCW voting rights were suspended in 2021, an unprecedented rebuke, following poison gas attacks on civilians in 2017.

Last year the watchdog blamed Syria for a 2018 chlorine attack that killed 43 people, in a long-awaited report on a case that sparked tensions between Damascus and the West.

Damascus has denied the allegations and insisted it has handed over its stockpiles.

Syria's civil war broke out in 2011 after the government's repression of peaceful demonstrations escalated into a deadly conflict that pulled in foreign powers and global jihadists.

The war has killed more than half a million people, displaced millions, and ravaged the country's infrastructure and industry.