KIRKUK, Iraq (Reuters) – More than 40 people suffered partial choking and skin irritation in northern Iraq when Islamic State fired mortar shells and Katyusha rockets filled with “poisonous substances” into their village late on Tuesday, local officials said.

None of the casualties died but five of them remain in hospital, said health officials in Taza, a mainly Shi’ite Turkmen village 12 miles south of the oil city of Kirkuk, in a region under Kurdish control.

“There were poisonous substances in these shells. We don’t know what,” Kirkuk province governor Najmuddin Kareem told reporters on a visit to the village on Wednesday.

A total of 24 shells and rockets were fired into Taza from the nearby Bashir area, said Wasta Rasul, a commander of the Kurdish peshmerga forces in the region.

The attack came as CNN reported that U.S. aircraft had begun targeting Islamic State’s chemical weapons sites near Mosul in Iraq, in an initial round of air strikes aimed at diminishing the militant group’s ability to use mustard agent.

An Islamic State detainee provided vital information that allowed the U.S. military to conduct the strikes, CNN said.

The ultra-hardline Sunni Muslim group seized large swathes of territory in northern and western Iraq in 2014.”Daesh wants to scare off the population,” said Kareem, using an Arabic acronym for Islamic State.

“They want to show they have chemical weapons just like the previous regime,” he said, referring to the chemical bombing of the Kurdish village of Halabja by Saddam Hussein’s forces in 1988, which left thousands of people dead.

(Reporting by Mustafa Mahmoud and Isabel Coles; Writing by Maher Chmaytelli; Editing by Dominic Evans and Gareth Jones)