The Syrian government's chemical weapons stockpile has been linked for the first time by laboratory tests to the largest sarin nerve agent attack of the civil war, diplomats and scientists told Reuters, supporting Western claims that government forces under President Bashar Assad were behind the atrocity.

The same test results were the basis for a report by the OPCW-United Nations Joint Investigative Mechanism in October that said the Syrian government was responsible for the Khan Sheikhoun attack, which killed dozens.

Russia has also denied that Syrian government forces have carried out chemical attacks and has questioned the reliability of the OPCW inquiries.

Under a U.S.-Russian deal after the Ghouta attack in 2013, Damascus joined the OPCW and agreed to permanently eliminate its chemical weapons program, including destroying a 1,300-ton stockpile of industrial precursors that has now been linked to the Ghouta attack.

Washington fired missiles at Shayrat in April 2017, saying the Syrian air force used it to stage the Khan Sheikhoun sarin attack on April 4 a few days earlier, killing more than 80 people.

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