Warplanes carried out a suspected toxic gas attack that killed at least 35 people including several children in a rebel-held town in northwestern Syria on April 4, opposition groups and a monitoring group said.
The Syrian Observatory for Human Rights said those killed in the town of Khan Sheikhun, in Idlib province, had died from the effects of the gas, adding that dozens more suffered respiratory problems and other symptoms.
Syrian girls, carrying school bags provided by UNICEF, walk past the rubble of destroyed buildings on their way home from school on March 7 in al-Shaar neighborhood, in the rebel-held side of the northern Syrian city of Aleppo. (IZEIN ALRIFAI/AFP/GImages)
The Observatory said medical sources in the town reported symptoms among the affected including fainting, vomiting, and foaming at the mouth.
The victims were mostly civilians, it said, and included at least nine children.
The pro-opposition Edlib Media Centre (EMC) posted a large number of photographs of people receiving treatment, as well as images showing what appeared to be the bodies of at least seven children in the back of a pick-up truck.
Photographs circulated by activists showed members of the volunteer White Helmets rescue group using hoses to wash down the injured, as well as at least two men with white foam around their mouths.
The Syrian National Coalition, an alliance of opposition groups whose leaders live in exile, accused President Bashar al-Assad's government of carrying out the gas attack and demanded a UN investigation.
"The National Coalition demands the Security Council convene an emergency session... to open an immediate investigation and take the necessary measures to ensure the officials, perpetrators, and supporters are held accountable," the body said in a statement.
Idlib province is largely controlled by an alliance of rebels including the Fateh al- Sham Front, a former al Qaeda affiliate previously known as the al- Nusra Front.
It is regularly targeted in strikes by the regime, as well as Russian warplanes, and has also been hit by the U.S.-led coalition fighting the Islamic State group, usually targeting jihadists.
Syria's government officially joined the Chemical Weapons Convention and turned over its chemical arsenal in 2013, as part of a deal to avert U.S. military action.
But there have been repeated allegations of chemical weapons use by the government since then, with a UN-led investigation pointing the finger at the regime for at least three chlorine attacks in 2014 and 2015.
The government denies the use of chemical weapons and has in turn accused rebels of using banned weapons.
The attack on April 4 comes only days after forces loyal to Assad were accused of using chemical weapons in a counter-offensive in neighboring Hama province.
U.S. Army Soldiers clean the outside of a CH-47 Chinook during detail aircraft decontamination training near Erbil, Iraq, Mar. 1, 2017. This training is part of the overall Combined Joint Task Force – Operation Inherent Resolve building partner capacity by training and improving the capability of partnered forces fighting ISIS in Iraq and Syria. (U.S. Army photo by Sgt. Josephine Carlson)
On March 30, air strikes on several areas in the north of Hama province left around 50 people suffering respiratory problems, according to the Observatory, which could not confirm the cause of the symptoms.
The monitor relies on a network of sources inside Syria for its information, and says it determines whose planes carry out raids according to type, location, flight patterns, and munitions used.
More than 320,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.
The April 4 gathering in Brussels has been billed as a follow-up to a donors' conference last year in London, which raised about $11 billion for humanitarian aid programs in the devastated country.