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A recent report by IHS Conflict Monitor, says the Islamic State (ISIL) has used chemical weapons, including chlorine and sulfur mustard agents, at least 52 times on the battlefield in Syria and Iraq since it swept to power in 2014. More than one-third of those chemical attacks have come in and around Mosul, the Islamic State stronghold in northern Iraq.

IHS, a London-based intelligence collection and analysis service, bases on local news reports, social media and Islamic State propaganda. According to the New York Times, that reported on it, the IHS assessment includes the location of the 52 reported chemical attacks.

American and Iraqi military officials have expressed growing alarm over the prospect of additional chemical attacks as the allies press to regain both Mosul and Raqqa, the Islamic State capital in Syria.

A military spokesman in Iraq, Colonel John Dorrian, said that the Islamic State’s ability to use chemical weapons is “rudimentary,” and that American, Iraqi and other allied troops are equipped to deal with the impact of these chemical attacks — typically rockets, mortar shells or artillery shells filled with chemical agents. The effects of these chemical munitions thus far have been limited to the immediate area where they land.

In an effort to blunt the Islamic State’s ability to make the weapons, the American-led air campaign has bombed militants associated with overseeing their production and the facilities where chemical ordnance is manufactured. As Iraqi forces now advance into Mosul, analysts warned that the Islamic State could unleash more chemical attacks as they cede control.

Columb Strack, a senior analyst and the head of the IHS Conflict Monitor said: “As the Islamic State loses ground around Mosul, there is a high risk of the group using chemical weapons to slow down and demoralize advancing enemy forces… And to potentially make an example of — and take revenge on — civilian dissidents within the city.”

According to Strack, most of the chemical weapons production equipment and experts were probably already evacuated to Syria, along with convoys of other senior members and their families.