?Chemical agent? in IS mortar fire Tests on Islamic State mortar fragments from fighting in Iraq show traces of chemical arms, the US military says.US Brig Gen Kevin Killea said they had found traces of chemical agent sulphur mustard on mortars used by IS to attack Kurdish forces in **rthern Iraq.But he said the tests were **t conclusive and final testing was due.US officials have been looking into reports that IS used chemical ****** mustard gas in an attack earlier this month in the town of Makhmour.