The head of ISIS’s chemical weapons unit who once worked for Saddam Hussein has been apprehended by American authorities — and admitted the group has mustard gas, official sources told The Post.

Sleiman Daoud al-Afari is being held at a temporary detention facility in Erbil, Iraq, where US military officials are grilling him about the Islamic State’s intentions to use deadly chemical and biological weapons, the sources said.

Defense Department officials described al-Afari as a “significant” ISIS leader who was nabbed in February by elite American commandos.

Since then, al-Afari has offered up crucial details about how the terror organization packed its artillery shells with powdered mustard gas, sources said.

One Defense official told The Post that although the mustard gas was not “concentrated enough” to snuff out a life, it could certainly impair someone.

After the US military has completed the interrogation process, al-Afari will be transferred to Iraqi and Kurdish authorities, sources said.

Al-Afari was a former employee of Iraqi despot Saddam Hussein’s Military Industrialization Authority.

Saddam was hanged in 2006 by the Iraqi government after being convicted of crimes against humanity.