The ISIS is behind a spate of mustard gas attacks in Syria and may have enough of the killer substance to slaughter tens of thousands, The Daily Mirror reported.
The network may have access to 20 tonnes of the evil weapon and could smuggle it out of Syria and into Europe, a leading expert in chemical warfare has warned.
"Evidence points to Islamic State behind the attacks and there could be more. There is evidence they used mustard gas, either stolen by Islamic State from (Syrian President Bashar) Assad or - and this is a real game changer - Islamic State made it themselves," Col (retd) Hamish de Bretton-Gordon said.
"This is horrific and the West must act to stop Islamic State now because the threat from them just became much greater and they could take huge areas they have not conquered before," he told the daily.
He warned that ISIS could smuggle mustard gas to attack Europe after finding a recipe on the 'dark web' - the murky and secretive area of the internet used by crooks.
"It is not easy to make mustard gas but it is possible and a lone wolf could get the information off the internet and dark web. If you tried to buy the precursors in the UK or US you would most likely be picked up," Bretton-Gordon said. "Could IS move mustard gas out of the Syria/Iraq theatre of war?
That is the real issue I expect," he said. Scores have died from chemical attacks in both Syria and Iraq in recent weeks and at the weekend Islamic State launched another suspected mustard gas attack. Col de Bretton-Gordon, who advises NGOs throughout Syria and elsewhere in the world, said, "The West is running out of time to do something about IS. We must act now."