Syria's all-weather friend Russia defended Bashar al-Assad government on Wednesday in the face of an international outcry over a suspected chemical attack that killed scores of civilians.
Justifying government's high-handedness, Russia said that a Syrian air strike hit a "terrorist warehouse".
The UN Security Council was to hold an emergency meeting later on Wednesday on the attack, which killed at least 72 civilians, among them 20 children, in the rebel-held town of Khan Sheikhun on Tuesday.
Washington and London have pointed the finger at President Bashar al-Assad's government for the attack, though the regime has denied any use of 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.
The ministry said the "arsenal of chemical weapons" was intended for fighters in Iraq, describing its information as "completely reliable and objective."
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". Others have 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 this morning, with airplanes carrying out strikes that released "toxic gas" on Khan Sheikun, 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.
Medic Hazem Shehwan told AFP he saw victims with "pinpoint pupils, convulsions, foaming at the mouth and rapid pulses".
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 Sheikun again on Wednesday morning, the Observatory said. There were no immediate details on a toll.
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 yesterday's attack. The UN's Commission of Inquiry for Syria said it had also begun investigating the "alleged use of chemical weapons".
Britain, France and the United States were to present a resolution to the Security Council today calling for the OPCW to quickly report findings on the attack.