Syria's opposition National Coalition accused President Bashar al-Assad's government of a suspected toxic gas attack Tuesday that killed at least 35 people, and demanded a UN investigation.
The attack on the town of Khan Sheikhun in Syria's northwestern Idlib province hit early on Tuesday, and left dozens of people suffering respiratory problems as well as fainting and vomiting, a monitor said.
The National Coalition called on the UN Security Council to "convene an emergency session..., 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," the statement added.
It accused the "regime of the criminal Bashar" of carrying out the attack, using "shells containing chemical gas".
The Britain-based Syrian Observatory for Human Rights said the dead were mostly civilians, among them nine children.
It said medical sources reported symptoms including fainting, vomiting and foaming at the mouth among the affected.