"For us, it is clear that such an obvious violation of international law cannot remain without consequences," Maas said in a statement following the release of the report by the Organisation for the Prohibition of Chemical Weapons (OPCW). "Those responsible must be held accountable."

The watchdog accused the Syrian regime of using chlorine in an attack on the town of Saraqib.

It is the second report by an investigations team set up by the OPCW, which has the new power to apportion blame for attacks.

OPCW investigators interviewed 30 witnesses, analysed samples collected at the scene, reviewed symptoms reported by victims and medical staff and examined satellite imagery to reach their conclusions, the Hague-based organisation said.

OPCW states will vote later this month on whether to impose sanctions on Syria, including the suspension of its voting rights in the organisation, over its failure to comply with its rules.

"All OPCW member states are now called to respond to these continuing violations by Syria of the Chemical Weapons Convention," Maas said, urging governments to "use the available means within the framework of the Convention to enforce its respect".

Syria has continued to deny the use of chemical weapons and insists it has handed over its weapons stockpiles under a 2013 agreement.