Islamic State (IS, formerly ISIS/ISIL) fighters used “poisonous substances” during the shelling of a village in northern Iraq on Tuesday, a local governor said, according to Reuters.

"There were poisonous substances in these shells. We don't know what," Kirkuk province governor Najmuddin Kareem told reporters, referring to a Tuesday attack on the village of Taza.

More than 40 people suffered from partial chocking and skin irritation after mortar shells and Katyusha rockets filled with the "poisonous substances" exploded in the mainly Shia Turkmen village, which is located south of the oil city of Kirkuk, in a region under Kurdish control.

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None of the 40 people died as a result of the attack, though five remain in hospital, health officials told Reuters.

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

It comes just one day after the Kurdish militia group YPG stated that Islamist opposition fighters used yellow phosphorous in a chemical attack on the Sheikh Maqsood neighborhood of Aleppo, Syria, on Tuesday.

Meanwhile, US aircraft have begun targeting IS' chemical weapons sites near Mosul, Iraq. It comes after an initial round of airstrikes aimed at diminishing the group's ability to use mustard agent, according to CNN.

It is unclear whether the strikes conducted over the past several days have been successful. The strikes were aided by an IS detainee who provided vital information to the US military, according to the news network.

Last month, a source from the Organization for the Prohibition of Chemical Weapons (OPCW) said that IS militants attacked Kurdish forces with mustard gas in 2015, citing lab tests that came back positive for the substance after Kurdish soldiers fell ill on the battlefield.

It represented the first known instance of chemical weapons use in Iraq since the fall of Saddam Hussein, the source said.

The revelation came just three days after Central Intelligence (CIA) Director John Brennan stated that IS had used chemical weapons on the battlefield, stressing that the militant group may have more in its possession.

In October, the OPCW also concluded that mustard gas was used in neighboring Syria in 2015. Experts believe the mustard gas used in Syria originated from an undeclared chemical stockpile, or that militants have gained the basic knowledge to develop and conduct a crude chemical attack with rockets or mortars.