Syria 'chemical attack' down to Assad, US says
The White House says it is "confident" Bashar al-Assad's government was behind an apparent chemical attack that killed at least 58 people in north-west Syria.
The Syrian Observatory for Human Rights reported that strikes on Khan Sheikhoun by Syrian government or Russian jets had caused many people to choke.
Later, aircraft fired rockets at local clinics treating survivors, medics and activists said.
Syria's army denied the government had used any such weapons.
In a statement, President Donald Trump condemned what he called "these heinous actions" by the Bashar al-Assad regime.
"It is clear that this is how Bashar al-Assad operates," the US Secretary of State Rex Tillerson said, "with brutal, unabashed barbarism."
The UK, United Nations and France, among others, also condemned the incident, which would, if confirmed, be one of the deadliest chemical attacks in Syria's civil war.
What witnesses saw
The warplanes are reported to have attacked rebel-held Khan Sheikhoun, about 50km (30 miles) south of the city of Idlib, early on Tuesday, when many people were asleep.
- Hussein Kayal, a photographer for the pro-opposition Edlib Media Center (EMC), told the Associated Press that he was awoken by the sound of an explosion at about 06:30 (03:30 GMT)
- When he reached the scene, there was no smell, he said, and he found people lying on the floor, unable to move and with constricted pupils
- Mohammed Rasoul, the head of a charity ambulance service in Idlib, told the BBC his medics had found people, many of them children, choking in the street
- The UK-based monitoring group, the Syrian Observatory for Human Rights (SOHR), quoted medics who had treated people for fainting, vomiting and foaming at the mouth
- An AFP news agency journalist saw a young girl, a woman and two elderly people dead at a hospital, all with foam still visible around their mouths
- The journalist also reported that the same facility was hit by a rocket on Tuesday afternoon, bringing down rubble on top of doctors treating the injured.
The source of the projectile was not clear, but the EMC and the opposition Local Co-ordination Committees (LCC) network said warplanes had targeted several clinics.
Aftermath of attack in pictures (Warning graphic images)
Pro-government journalists later cited military sources as saying there had been an explosion at an al-Qaeda chemical weapons factory in Khan Sheikhoun that was caused either by an air strike or an accident.
The defence ministry of Russia, President Assad's ally, insisted it had not carried out any air strikes in the vicinity.
How many victims are there?
The SOHR put the death toll at 58, including 11 children, but Mr Rasoul reported that 67 people had been killed and 300 injured.
The pro-opposition Step news agency said 100 had died.
One aid agency, the Union of Medical Care and Relief Organisations (UOSSM), put the death toll at more than 100.
The EMC said it had stopped counting the victims because there were so many.
What substance was used?
The SOHR said it was unable to say what exactly was dropped.
However, the EMC and LCC said it was believed to be the nerve agent Sarin, which is highly toxic and considered 20 times as deadly as cyanide.
Chemical weapons expert Dan Kaszeta said that determining whether Sarin was involved simply by examining video clips is problematic.
He added that Tuesday's attack could have been the result of one of any number of chemical agents as they tend to "behave the same in terms of their physiological effects on the human body".
Sarin is almost impossible to detect because it is a clear, colourless and tasteless liquid that has no odour in its purest form.
Syria's army, in a statement posted on state news agency Sana, said it never had and never would use poison gas.
Has Sarin been used in Syria before?
The government was accused by Western powers of firing rockets filled with Sarin at rebel-held suburbs of Damascus in August 2013, killing hundreds of people.
President Assad denied the charge, blaming rebel fighters, but he did subsequently agree to destroy Syria's chemical arsenal.
Despite that, the Organisation for the Prohibition of Chemical Weapons (OPCW) has continued to document the use of toxic chemicals in attacks in Syria.
In January 2016, it said blood samples taken from the victims of one unspecified attack showed victims had been exposed to Sarin or a Sarin-like substance.
Other reported use of chemical agents:
- A joint investigation with the UN concluded in October that government forces had used chlorine as a weapon at least three times between 2014 and 2015
- It also found Islamic State militants had used the blister agent sulphur mustard
- Human Rights Watch also recently accused government helicopters of dropping bombs containing chlorine on rebel-held areas of Aleppo
What has been the reaction?
- "Today's chemical attack in Syria against innocent people, including women and children, is reprehensible" - US President Donald Trump
- UN Syria envoy Staffan de Mistura said it was a "horrific" attack and that there should be a "clear identification of responsibilities and accountability" for it; the UN Security Council is to hold an emergency meeting on Wednesday
- "Once again the Syrian regime will deny the evidence of its responsibility for this massacre," French President Francois Hollande said
- UK Foreign Secretary Boris Johnson said that President Bashar al-Assad would be guilty of a war crime if it were proved his regime was responsible
- The OPCW said it was "seriously concerned", adding that it was "gathering and analysing information from all available sources".