Syria conflict: 'Chemical attack' in Idlib kills 58

At least 58 people have been killed and dozens wounded in 
a suspected chemical attack on a rebel-held town in north-western Syria, a monitoring group says.

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.

The Syrian government has repeatedly denied using 
chemical weapons.

If confirmed, it would be one of the deadliest chemical
 attacks in Syria since the civil war began six years ago.

What happened?

The warplanes are reported to have attacked Khan 
Sheikhoun, about 50km (30 miles) south of the city of Idlib, early on Tuesday, when many people were asleep.

Mohammed Rasoul, who is in charge of a charity ambulance
service in Idlib, told local media that he heard of the air strikes at about 06:45 (03:45 GMT) and that his medics found people
choking in the street when they arrived 20 minutes later.

"The situation over there is very bad, and most of those who are suffering are children," he said.

The Syrian Observatory quoted medics as saying that they had been treating people with symptoms including 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 pro-opposition Edlib Media Center (EMC) reported that warplanes had targeted several local clinics.

How many victims are there?

The Syrian Observatory put the death toll at 58, including 11
children, but Mr Rasoul reported that 67 people had been 
killed and that 300 were injured.

The pro-opposition Step news agency meanwhile said 100 had died.

The EMC said it had stopped counting the victims because there were so many.

It posted photos showing what appeared to be at least 
seven dead children in the back of a pick-up truck. There 
were no visible traumatic injuries on their bodies.

What substance was used?

The Syrian Observatory said it was unable to say what 
exactly was dropped.

However, the EMC said it was believed to be the nerve
 agent sarin, which is highly toxic and considered 20 times as deadly as cyanide.

As with all nerve agents, sarin inhibits the action of the
acetylcholinesterase enzyme, which deactivates signals
 that cause human nerve cells to fire. This blockage pushes nerves into a continual "on" state. The heart and other muscles - including those involved in breathing - spasm.

Sufficient exposure can lead to death via asphyxiation within
minutes.

Has sarin been used in Syria before?
The government was accused by Western powers of firing
rockets filled with sarin at several rebel-held suburbs of the capital Damascus in August 2013, killing more than 500 people.

President Bashar al-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  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.

What about other 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 on at least eight occasions between 17
November and 13 December, during the final stages of the battle for the city.

And last week, two suspected chemical attacks were 
reported in Hama province, in a rebel-held area not far from Khan Sheikhoun.

What has been the reaction to Tuesday's attack?

Idlib province, where the air strikes took place, is largely
controlled by an alliance of rebel factions and the al-Qaeda-linked jihadist group, Hayat Tahrir al-Sham.

The region is regularly targeted in air strikes by the government and its ally Russia, as well as the US-led multinational coalitionagainst IS.

There was no immediate comment from the government on
Tuesday, but a Syrian military source told Reuters news agency
that it "does not and has not" used chemical weapons.

The opposition National Coalition accused the government
 of being behind what it called a "horrible crime", and called on the UN Security Council to order an immediate investigation.

"Failure to do so will be understood as a message of 
blessing to the regime for its actions," it warned in a statement.