How chemical weapons have helped bring Assad close to victory
After seven devastating years of civil war in Syria, which have left more than 350,000 people dead, President Bashar al-Assad appears close to victory against the forces trying to overthrow him.
So how has Mr Assad got so close to winning this bloody, brutal war?
A joint investigation by BBC Panorama and BBC Arabic shows for the first time the extent to which chemical weapons have been crucial to his war-winning strategy.
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Source: BBC Panorama and BBC Arabic research. Map built with Carto.
The BBC has determined there is enough evidence to be confident that at least 106 chemical attacks have taken place in Syria since September 2013, when the president signed the international Chemical Weapons Convention (CWC) and agreed to destroy the country's chemical weapons stockpile.
Syria ratified the CWC a month after a chemical weapons attack on several suburbs of the capital, Damascus, that involved the nerve agent Sarin and left hundreds of people dead. The horrific pictures of victims convulsing in agony shocked the world. Western powers said the attack could only have been carried out by the government, but Mr Assad blamed the opposition.
The US threatened military action in retaliation but relented when Mr Assad's key ally, Russia, persuaded him to agree to the elimination of Syria's chemical arsenal. Despite the Organisation for the Prohibition of Chemical Weapons (OPCW) and the United Nations destroying all 1,300 tonnes of chemicals that the Syrian government declared, chemical weapons attacks in the country have continued.
"Chemical attacks are terrifying," said Abu Jaafar, who lived in an opposition-held part of the city of Aleppo until it fell to government forces in 2016. "A barrel bomb or a rocket kills people instantly without them feeling it... but the chemicals suffocate. It's a slow death, like drowning someone, depriving them of oxygen. It's horrifying."
But Mr Assad has continued to deny his forces have ever used chemical weapons.