Doctors working in the besieged Syrian town of Aleppo warned that the use of chemical weapons is becoming the new normal in the conflict, after reports of yet another chlorine gas attack killed three people and injured dozens more.

The United Nations envoy to Syria, Staffan de Mistura, did not confirm the attack though admitted there was evidence that such an incident had taken place. “If it did take place, it is a war crime and as such it would require everyone … to address it immediately,” he said.

Doctors working in Aleppo though said the attack, which took place after Syrian opposition fighters made an apparent breakthrough against the government siege on the city, was becoming the “new normal” in Syria.

“Since the UN security council resolution to destroy chemical weapon stockpiles in Syria, there were more than 70 attacks with chemical agents by the Syrian regime but this time with chlorine gas,” said Zaher Sahloul from the Syrian American Medical Society, which has worked in Aleppo.

“Using chemical agents without accountability has become the new normal in Syria,” he said.

“It is a very dangerous precedent that the international community is setting.”

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