A suspected chemical attack killed dozens of people in a rebel-held area of Syria on Tuesday, activists said, describing an incident that would mark one of the worst of its kind in Syria’s six-year civil war.
At least 58 people, including 11 children, died in the incident in northern Idlib province, southwest of Aleppo, said the British-based Syrian Observatory for Human Rights. The death toll “is expected to rise” because more than 160 people were injured, many experiencing severe symptoms, the group added.
White House Press Secretary Sean Spicer told reporters that the chemical attack is “reprehensible and cannot be ignored by the civilized world.”
He blamed it on both the regime of Syrian President Bashar al-Assad and the Obama administration’s “weakness and irresolution” to act after initially citing the use of chemical weapons as a “red line.”
But the Syrian government denied any involvement and said it was complying by an international Chemical Weapons Convention that bans such instruments of war, according to SANA, the Syrian state-run news agency.
Instead, the government is blaming “armed terrorist organizations” for the attack. “The Syrian Arab republic stresses that all those fabricated allegations will not prevent it from continuing its war on terrorism … and from working for a political solution to the crisis in Syria,” SANA reported.
Related: Syrian Government Blamed for Third Chemical Attack: Report
The pro-opposition Idlib Media Center also said dozens of people had been killed Tuesday, according to The Associated Press. It posted pictures to Facebook showing children who either appeared to be dead or incapacitated.
The White Helmets volunteer group shared images of its members spraying children with a hose.
British leaders condemned any use of chemical weapons, with Prime Minister Theresa May describing it as “barbarism.”
“I am horrified by the reports of an attack near Idlib in Syria,” added British Foreign Secretary Boris Johnson in a statement. “The reports we are receiving strongly suggest the use of chemical weapons. And although we cannot yet be certain about what has happened, this bears all the hallmarks of an attack by the regime which has repeatedly used chemical weapons. ”
Israeli Prime Minister Binyamin Netanyahu tweeted he was “shocked and outraged” by the pictures.
Secretary of State Rex Tillerson ignored question from reporters when asked about the apparent slaughter.
None of the images, nor the attack itself, have been verified by NBC News.
Assad’s regime in Damascus released no official statement following the reports, but a senior military officer told NBC News on condition of anonymity that the government was not responsible.
“These allegations are null and void. Syrian or Russian jets never used chemical weapons during their fight against terrorism,” the officer said, who requested anonymity because he was not authorized to speak with the media. “Syrian forces and its allies target terrorist groups, not civilians,” adding that his country would “continue the fight against terror until victory is accomplished.”
It was the third claim of a chemical attack in just over a week in Syria, according to the AP. The previous two were reported in Hama province, in an area not far from Khan Sheikhoun, the site of Tuesday’s alleged attack.
The latest reports come on the eve of a major international meeting in Brussels on the future of Syria and the region.
Staffan de Mistura, the U.N. Special Envoy for Syria, said the U.N. Security Council will meet Wednesday as part of an effort to identify who is responsible.
“It’s true, every time we have a moment in which the international community is capable of being together — 70 countries tomorrow — there is someone, somehow, that tries to undermine that feeling of hope by producing a feeling of horror and outrage,” De Mistura said, “but we are not going to give up.”
Activists told the AP it was the worst since the 2013 sarin nerve gas attack on the Damascus suburb of Ghouta that killed hundreds of civilians. That event prompted Assad to agree to destroy Syria’s chemical weapons following an international outcry.
The government has consistently denied using chemical weapons and chlorine gas, accusing the rebels fighting to depose Assad of deploying it in the war instead.
Related: Syria Chlorine Attack Reports Raise Questions About Loopholes
In 2015, the Security Council established the Organization for the Prohibition of Chemical Weapons-United Nations Joint Investigative Mechanism, or JIM, to root out those responsible for chemical attacks in Syria.
“Civilians are facing on one hand the grotesque tactics of ISIS and on the other hand airstrikes from the Syrian regime and others,” said Oliver Money, the director of the aid organization International Rescue Committee. “They’re trapped between these two forces just wanting a semblance of life. And today’s attack is an awful reminder of that.”