IS chemical weapons capability 'significantly degraded': report

The militant group, however, likely retains expertise in producing small batches of sulfur mustard and chlorine agents, a report by IHS Markit said, adding that there has been major reduction in IS' use of chemical weapons outside the northern Iraqi city.

IS carried out one chemical weapons attack in Syria this year, while all other recorded allegations of chemical agent use were in Iraq, including nine inside Mosul and one in Diyala province, the report found.

"The operation to isolate and recapture the Iraqi city of Mosul coincides with a massive reduction in Islamic State chemical weapons use in Syria," said Columb Strack, senior Middle East analyst at IHS Markit.

"This suggests that the group has not established any further chemical weapons production sites outside Mosul, although it is likely that some specialists were evacuated to Syria and retain the expertise."

IHS Markit said the militant group has been accused of using chemical weapons at least 71 times since July 2014 in Iraq and Syria. Most of these involved either the use of chlorine or sulfur mustard agents, delivered with mortars, rockets and IEDs.

The report released on Tuesday says the continuing chemical weapons attacks in Mosul most likely draw on remaining stockpiles in the city.

It warned, however, that the extremist group likely retains the capability to produce small batches of low quality chlorine and sulfur mustard agents elsewhere.

IS militants could use such agents to enhance the psychological impact of suicide car bombings in urban areas or in terrorist attacks abroad.

The militant group has lost more than half the territory it once controlled in Iraq. It's now fighting to defend a cluster of western neighbourhoods in Mosul, Iraq's second-largest city.

Mosul is the last major urban area held by the group in Iraq, and is believed to be at the heart of its efforts to produce chemical weapons.