The OPCW has said its data provided "reasonable grounds" an attack took place, but assigned no blame.
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Suspected Syria chemical attack
The suspects in the Novichok poisoning and their superiors are hit with EU sanctions.
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The US and UK say Syria and Russia made up a story of a chlorine gas attack in Aleppo in November.
Read moreMoscow targets rebels near Aleppo after accusing them of launching a chemical attack on the city.
Read moreAbdul Hamid Youssef describes how he lost his wife, his twins and other family members in a chemical attack.
How chemical weapons have helped bring Assad close to victory
After seven years of civil war in Syria, President Bashar al-Assad appears close to victory against the forces trying to overthrow him.
A BBC investigation shows the extent to which chemical weapons have been crucial to his war-winning strategy.
Nawal al-Maghafi
BBC News, Hudayda
A BBC investigation has found that at least 106 chemical attacks have taken place since mid-2014.
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Activists allege that government forces dropped bombs filled with chemicals on rebel-held Douma.
Read moreA suspected chemical attack in Douma in April reportedly left dozens of civilians dead and caused an international outcry.
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Jonathan Marcus
Diplomatic correspondent
The OPCW's new powers to assign blame are likely to raise tensions between world powers.
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