At least 85 people were killed in the chlorine gas attack in a Syrian rebel-held town of Douma, near the capital, Damascus, on Saturday.
Among those killed were many women and children who had sought refuge in the basements of buildings to escape heavy bombardment by pro-government forces, according to a statement by rescue workers and medical staff.
Commenting on the incidents, the European Union called for an international response to the attack.
“The evidence points towards yet another chemical attack by the regime,” the bloc said in a statement.
“It is a matter of grave concern that chemical weapons continue to be used, especially on civilians. The European Union condemns in the strongest terms the use of chemical weapons and calls for an immediate response by the international community.”
The EU also called on the UN Security Council to re-establish its checks to identify the perpetrators of chemical attacks and on Russia and Iran – the Syrian government’s closest allies – to use their influence with al-Assad to prevent further attacks.
Meanwhile, French Foreign Minister Jean-Yves Le Drian said France strongly condemned attacks and bombings by Syrian government forces in the last 24 hours in Douma, adding they were a “gross violation of international humanitarian law.
He called for the United Nations Security Council to meet quickly to examine the situation saying that France would work with allies to verify reports that chemical weapons were used.
Referring to President Emmanuel Macron’s warning that France could strike unilaterally if there was a deadly chemical attack, Le Drian said that Paris would assume all its responsibilities in the fight against the proliferation of chemical weapons.
In recent years, the Syrian government has been accused of using chemical weapons as a tool against the armed opposition.