Up to 100 men, women and children have died and dozens more battling injuries after the deadliest chemical weapons attack in Syria since 2013.
Syrian forces are suspected to be behind the attack on the rebel-held town of Khan Sheikhoun in the Idleb province, but the Syrian military have denied responsibility, saying they would never use chemical weapons.
"We deny completely the use of any chemical or toxic material in Khan Sheikhoun town today and the army has not used nor will use in any place or time neither in past or in future," the Syrian army command said in a statement.
The World Health Organisation (WHO) confirmed in a statement released on Tuesday the symptoms of those affected by the attack appear to show signs the chemicals used included deadly nerve agents banned by international law.
"The likelihood of exposure to a chemical attack is amplified by an apparent lack of external injuries reported in cases showing a rapid onset of similar symptoms, including acute respiratory distress as the main cause of death. Some cases appear to show additional signs consistent with exposure to organophosphorus chemicals, a category of chemicals that includes nerve agents," the statement read.
Dr Peter Salama, Executive Director of the WHO Health Emergencies Programme, said: "The images and reports coming from Idleb today leave me shocked, saddened and outraged. These types of weapons are banned by international law because they represent an intolerable barbarism."
The U.S. Government believes the chemical agent sarin was used in the attack and it was "almost certainly" carried out by forces loyal to President Bashar al-Assad, a U.S. Government source told Reuters.
Sarin is a colourless, odourless liquid and is generally considered to be a weapon of mass destruction. Production and stockpiling of sarin was outlawed in 1997.
WARNING: Graphic images.
In the hours following the attack, one of the medical clinics treating victims was hit by an airstrike. Victims had been sent to small clinics, as the region's main hospital had been severely damaged in an airstrike two days earlier.
While the full extent of deaths has not been confirmed, the Syrian Observatory for Human Rights said at least 58 people, including 11 children, had been killed and 160 more were injured. The head of the health authority in Idlib said more than 50 had died and 300 wounded, while the Union of Medical Care Organizations said there were at least 100 fatalities.
It is the first major atrocity which the Syrian Government has been accused of since President Donald Trump came to office. The US Government has responded by blaming the attack on the the Obama administration, accusing it of "weakness and irresolution" in the face of the Syrian crisis.
Medics, activists and witnesses on the ground said that the air strikes caused people to suffocate, while others spasmed, went pale and gasped for air, according to British-based Syrian Observatory for Human Rights sources.
The organisation's Director, Rami Abdulrahman, told Reuters they believed the Syrian regime was behind the attack due to the types of aircraft used in the air strike, which included Sukhoi 22 jets -- fighter-bomber planes made by Russia.
If confirmed, the gas attack would be the nation's deadliest since almost 1,500 people were killed in a sarin attack near Damascus on 21 August 2013. The US Government also attributed that attack to the Syrian Government, issuing a rare release detailing how the attack took place from information gleaned by US spy agencies.
The release claimed that the Syrian Government has large stockpiles of outlawed chemical agents, including mustard gas, sarin and VX and also has thousands of weapons used to deliver the chemical weapons.
"Syrian President Bashar al-Asad is the ultimate decision maker for the chemical weapons program and members of the program are carefully vetted to ensure security and loyalty," the 2013 release claimed.
"We assess with high confidence that the Syrian regime has used chemical weapons on a small scale against the opposition multiple times in the last year, including in the Damascus suburbs."
The chemical weapons attack is one of many air strikes to hit rebel-held areas of Syria in recent days, with Syrian warplanes battering east Damascus with up to 100 airstrikes in 24 hours on Tuesday.
The bombardment follows an attempt by the Syrian government to cut the region's vital food and medical supplies in order to cripple Rebel forces.
ALSO ON HUFFPOST AUSTRALIA