Russia has claimed that the gas was released after Syrian government forces hit a rebel chemical weapons depot
The UN Security Council is meeting later today to discuss a suspected chemical weapons attack in Syria which killed dozens of people.
The Union of Medical Care Organizations – a coalition of international aid agencies that funds hospitals in Syria – has reported that at least 100 people were killed in the attack while the Syrian Observatory for Human Rights has put the death toll at 58.
Women, children and babies are believed to be among the dead - and approximately 400 people have been injured.
Russia has claimed that the gas was released after Syrian government forces hit a rebel chemical weapons depot.
The UK, France and the US have proposed a UN Security Council resolution to condemn the attack.
The resolution calls on the Organisation for the Prohibition of Chemical Weapons to quickly reveal its findings on the attack and "condemns in the strongest terms the use of chemical weapons" in Syria.
It expresses "outrage" over the use of toxic gases in the six-year war.
It also calls on UN Secretary-General Antonio Guterres to report monthly on whether the Syrian government is co-operating with an international inquiry into the use of chemical weapons across the war-torn country.
Diplomats say the resolution is likely to be put to a vote when the UN Security Council holds an emergency meeting on Wednesday.
Distressing footage from the town of Khan Sheikhoun – where the attack occurred yesterday – showed people choking and fainting in the aftermath of the attack - with some victims left foaming at the mouth.
Rescue workers hosed down children to wash away any chemicals from their skin and gave them oxygen.
Mohammed Hassoun, an activist in nearby Sarmin, said: "Because of the number of wounded, they have been distributed around in rural Idlib.
"They were unconscious, they had seizures and when oxygen was administered, they bled from the nose and mouth," he said,
Other videos showed dead children being covered with blankets, and bodies being loaded into trucks.
The Syrian Observatory for Human Rights says the attack was believed to have been carried out by government jets, but the Syrian military has denied responsibility and said it would never use chemical weapons.
Russia's defence ministry has also denied carrying out any airstrikes in the area.
While the attack has been met with international condemnation, the United States' response to the strike has been criticised.
In a statement, President Trump called the assault "reprehensible" - but took the unusual step of saying that Barack Obama's strategy for Syria was partly to blame.
"These heinous actions by the Bashar al Assad regime are a consequence of the past administration's weakness and irresolution," Mr Trump wrote.
US Secretary of State Rex Tillerson said Russia and Iran bore "great moral responsibility" for the bloodshed caused by the chemical attack.
White House officials including Press Secretary Sean Spicer had suggested in recent days that President Assad's departure was not necessary for peace - and Syrians should be able to decide his fate.
But Republican Senator John McCain said the latest chemical attack showed otherwise, adding: "In case it was not already painfully obvious: the notion that the Syrian people would be able to decide the fate of Assad or the future of their country under these conditions is an absurd fiction.
"The recent statements by US officials suggesting otherwise only serve to legitimise the actions of this war criminal in Damascus."
Samantha Power, former US ambassador to the UN, tweeted: "Backed by Russia and Iran, declared permanent by Trump, Assad regime in Syria feels safe to do what it wants. Gassing people is what it wants."
Backed by Russia&Iran, declared permanent by Trump, Assad regime in #Syria feels safe to do what it wants. Gassing people is what it wants.— Samantha Power (@SamanthaJPower) April 5, 2017
The UK is co-hosting a major aid-pledging conference for Syria later on Wednesday, with Foreign Secretary Boris Johnson and International Development Secretary Priti Patel attending the event in Brussels.
Mr Johnson has said he is determined for the conference to "step up international assistance to the most vulnerable people affected by the conflict."
Idlib province is almost entirely controlled by the Syrian opposition and is home to 900,000 people displaced by the war.
Rebels, including former al Qaeda affiliates, have vowed to avenge the apparent gas attack, calling on fighters to "ignite all the fronts."
Additional reporting from IRN ...