Russia defended its ally Damascus on Wednesday against international outcry over a suspected chemical attack that killed scores of civilians, saying a Syrian air strike hit a "terrorist warehouse".
At least 72 civilians, among them 20 children, were killed in Tuesday's attack in rebel-held Khan Sheikhun, and dozens more were left gasping for air, convulsing, and foaming at the mouth, doctors said.
The UN Security Council was to hold an emergency meeting later Wednesday on the attack, with Britain, France and the United States pushing a resolution demanding a swift investigation.
Washington and London have pointed the finger at President Bashar al-Assad's government for the attack, though the regime has denied using chemical weapons.
Moscow, which launched a military intervention in 2015 in support of Assad's forces, said the deaths were caused when a Syrian air strike hit a "terrorist warehouse" containing "toxic substances".
The Russian defence ministry said in a statement that the building housed "a warehouse making bombs, with toxic substances", without saying if the strike was accidental or deliberate.
Syria's army had earlier denied any use of chemical weapons, saying it "has never used them, any time, anywhere, and will not do so in the future."
Its denials have done little to quiet international condemnation, with UN chief Antonio Guterres on Wednesday saying the "horrific events" showed that "war crimes are going on in Syria".
Pope Francis said he was "horrified" by the "unacceptable massacre... where dozens of defenseless people, including many children, were killed."
Others blamed Damascus more directly for the attack, including British Foreign Secretary Boris Johnson who said "all the evidence I have seen suggests this was the Assad regime."
US Secretary of State Rex Tillerson also pointed the finger at the regime, saying "it is clear that this is how Bashar al-Assad operates: with brutal, unabashed barbarism."
If confirmed, the attack would be among the worst incidents of chemical weapons use in Syria's brutal civil war, which has killed over 320,000 people since it began in March 2011.
It unfolded in the early hours of Tuesday morning, with airplanes carrying out strikes that released "toxic gas" on Khan Sheikhun, in the northwestern province of Idlib, according to witnesses and a monitoring group."We ran inside the houses and saw whole families just dead in their beds," resident Abu Mustafa told AFP of the attack's aftermath.
"Children, women, old people dead in the streets."
The Syrian Observatory for Human Rights, a Britain-based monitor, said at least 160 people suffered the effects of the gas, with medical sources reporting incidents of vomiting, fainting, breathing problems and foaming at the mouth.
Medics worked frantically in the hours after the attack to treat a steady stream of patients, administering oxygen and hosing down victims to wash off chemical residue.
Even as they worked, air strikes hit a medical facility treating victims, an AFP correspondent said, bringing rubble down on top of medics and patients.
Air strikes hit Khan Sheikhun again on Wednesday morning, the Observatory said. There were no immediate details on a toll.
Idlib province is controlled mostly by an alliance of rebel and jihadist groups, including the former Al-Qaeda affiliate known as Fateh al-Sham Front.
Syria officially relinquished its chemical arsenal and signed the Chemical Weapons Convention in 2013, to avert military action after it was accused of an attack outside Damascus that killed hundreds.
But there have been repeated allegations of chemical weapons use since, with a UN-led investigation pointing the finger at the regime for at least three chlorine attacks in 2014 and 2015.
The Organisation for the Prohibition of Chemical Weapons (OPCW) said it was "seriously concerned" by reports of Tuesday's attack.
Britain, France and the United States were to present a resolution to the Security Council Wednesday calling for the OPCW to quickly report findings on the attack.
But it was unclear if Russia would veto the measure, as it has often done with previous Security Council resolutions concerning Syria.
The text calls on Syria to provide flight plans, flight logs and other information on its military operations on the day of the assault.
Successive rounds of peace talks aimed at ending Syria's civil war have failed to produce results, and Syria's opposition warned Tuesday that the attack cast doubt on the prospects for future negotiations.
Donor nations were meanwhile meeting for a second day in Brussels at a conference hosted by the European Union and United Nations to raise new funds for Syrian refugees, whose number now tops five million.
Over half Syria's population has been displaced internally and abroad since the conflict began, with regional neighbours hosting most of those who have become refugees.