A suspected chemical attack in a rebel-held Syrian town killed 100 people and injured 400 others, a medical relief group said, and some medics treating the wounded were later struck by rubble when an aircraft reportedly bombed a hospital.
"The army command categorically denies using any chemical or toxic substance in Khan Sheikhun today", said a statement carried by the state news agency SANA. The U.N. Security Council was expected to meet on Wednesday to discuss the incident.
In a Skype interview, he said doctors are struggling to deal with the victims, amid a shortage of facilities and medical supplies, and the antidote used to save patients, Pralidoxem, is in short supply.
The conference, also to be attended by aid and development groups, follows reports Tuesday that a suspected chemical attack killed dozens in northern Syria.
Syria's peace talks got off to a rocky start yesterday when rebel groups refused to meet President Bashar al-Assad's government and a war of words broke out between the two sides.
It was the third claim of a chemical attack in just over a week in Syria.
Following the 2013 attack, Syria joined the worldwide Chemical Weapons Convention under a US-Russian deal, averting the threat of US-led military intervention.
Mr Rycroft said an emergency council meeting would "shine a spotlight on the heinous use of chemical weapons yet again" in Syria, rally support for action in the council, and put pressure on Russian Federation and China "to hold to account those who used chemical weapons".
The White House condemned what it said was a "reprehensible" attack carried out by Assad s forces.
The attack came just ahead of the opening of a planned worldwide meeting of United Nations members, European Union members and some financial institutions throughout the world to discuss the current state and future of Syria.
Almost 400,000 people have been killed during the six years of the Syrian conflict, while half of the country's population has been displaced by the violence.
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The army again denied using chemical weapons on Tuesday, insisting "it has never used them, any time, anywhere, and will not do so in the future".
Idlib province is nearly entirely controlled by the Syrian opposition and is home to 900,000 people displaced from other areas by the 6-year-old war.
On Twitter, the head of the opposition High Negotiations Committee Riad Hijab said the attack was "evidence that it is impossible to negotiate with a regime addicted to criminal behaviour".
Horrific reports of chemical weapons attack in Idlib, Syria. Western states said the Syrian government was responsible for the 2013 attack.
A chemical attack, delivered Tuesday via an airstrike, killed at least 58 people, including children young enough to still be wearing diapers, in a rebel-controlled province along the Turkish border, various media reported.
August 24, 2016: The joint OPCW-U.N. panel determines the Syrian government twice used helicopters to deploy chlorine gas against its opponents, in civilian areas in the northern Idlib province.
The Organisation for the Prohibition of Chemical Weapons (OPCW), based in The Hague, meanwhile also said it was "gathering and analysing information from all available sources" about the attack.
"Italy will be at the forefront criticism of the attack at an emergency meeting of the United Nations Security Council requested by France and Britain", he went on.
"I've seen the reports about the use of sarin and as far as I know they have not been confirmed", he said.