WASHINGTON - A senior Islamic State of Iraq and Syria (ISIS) commander and top aide to Abu Bakr al-Baghdadi was killed in an coalition airstrike in Mosul earlier this week, U.S. officials said

Fadhil Ahmad al-Hayali, also known as Abu Muslim al-Turkomani and Hajji Mutazz, a former colonel in Saddam Hussein's intelligence directorate, was killed in a targeted airstrike on Tuesday. Pictures circulating on social media purportedly showed the body of al-Hayali.

NSC spokesperson Ned Price confirmed al-Hayali's death in a statement Friday. ISIS has not commented on the reports.

Also on Friday, a senior U.S. military officer said preliminary tests also show traces of the chemical agent sulfur mustard on mortars that Islamic State of Iraq and Syria militants used to attack Kurdish forces in Iraq.

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U.S. Brig. Gen. Kevin Killea, chief of staff for the military operations in Iraq and Syria, says the field testing is not conclusive, so final tests are underway to get the full make-up of the chemicals on the fragments.

Booking photo of Fadhil Ahmad al-Hayali, also known as Abu Muslim al-Turkomani and Hajji Mutazz from Camp Bucca.

U.S. officials have been looking into reports that ISIS militants used the chemical weapon mustard gas in the August 11 attack in Makhmour. Similar reports surfaced in July.

Killea told Pentagon reporters on Friday that Kurdish forces brought the mortar fragments to U.S. forces for testing, so there may be questions about the chain of custody of the evidence.

Last week, a senior Defense Department official told CBS News that the reports of mustard gas use were "credible" but the Pentagon later dialed back that report.