At least 58 people, including 11 children, died in a suspected gas attack in Syria’s northwestern Idlib province, local sources reported on Tuesday.
According to the Syrian Observatory for Human Rights (SOHR), people choked or fainted after the attack, while some were seen foaming at the mouth.
The SOHR said it had received the reports from medics on the ground in the town of Khan Sheikhoun.
Hours later, a small field hospital in the region was struck and destroyed, according to a civil defence worker in the area.
The Syrian National Coalition (SNC), the main opposition group, said planes from President Bashar al Assad’s military carried out the airstrikes.
It was not immediately clear if the deaths had been caused by the chemical weapons or injuries sustained in the airstrikes.
Videos purporting to show the aftermath circulated on social media.
One showed the bodies of several young children being covered with a blanket, while another showed men lifting a body into the back of a truck.
In a number of videos, medics could be seen helping people who appeared to have breathing difficulties.
Rescue workers were pictured hosing down children.
More than 60 people were reportedly injured in the airstrikes.
“At 18 cases had been taken to a hospital in Sarmin town. Because of the number of wounded, they have been distributed around in rural Idlib,” local media activist Mohammed Hassoun said.
“They were unconscious, they had seizures and when oxygen was administered, they bled from the nose and mouth.”
Russia’s defence ministry said it had not carried out any airstrikes in the area.
The Syrian government did not immediately comment on the allegations, but last week said claims the government was using chemical weapons were “devoid of truth”.
The SNC called for an emergency session of the UN Security Council, blaming the airstrikes on the “regime of the criminal Bashar”.
It urged the UN to “open an immediate investigation and take the necessary measures to ensure the officials, perpetrators and supporters are held accountable”.
“Failure to do so will be understood as a message of blessing to the regime for its actions,” it added.
France later also said that it wanted an emergency Security Council meeting.
“The perpetrators must be held accountable. We need to address this issue at the Security Council, as soon as possible,” Alexis Lamek, Deputy Permanent Representative of France to the UN, said.
British Foreign Secretary Boris Johnson said: “This bears all the hallmarks of an attack by the regime, which has repeatedly used chemical weapons.”
“If this is shown to be the work of the regime, it is further evidence of the atrocities perpetrated against the Syrian people over six years of appalling conflict,” Johnson said.
Idlib province is almost entirely controlled by the Syrian opposition and is home to 900,000 people displaced from other areas by the 6-year-old war.
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