A chemical weapons specialist working for the ISIS in Iraq has been captured by the US special forces in a raid and is being interrogated for weeks on the terror group’s capabilities and planning, officials revealed on Wednesday.

Sulayman Dawud al-Bakkar, the detainee as identified by those associated with the operation, was an expert on chemical and biological weapons for Iraq’s fallen president, Saddam Hussein.

Al Bakkar was expected to be handed over to the Iraqi government at the end of this week. A spokesperson for Pentagon told BBC that US had begun operations in Iraq, which was part of more aggressive actions to counter the ISIS, which has established strongholds in Syria and Iraq and is now expanding into Libya.

The New York Times reported that the US interrogators have already been able to gather information from the man as to how the ISIS loaded mustard gas into shells. The ISIS have used mustard gas twice against the Kurdish forces and once against anti-Assad forces in northern Syria. Mustard gas or sulfur mustard is a chemical warfare agent which if comes in contact with exposed skin causes large blisters. It also affects lungs badly if inhaled.

“He is the technical expert on the chemical weapons project, but Taha Rahim al-Dulaimi is the ideological driver of this,” the Guardian quoted Hisham al-Hashimi, an Iraqi author and academic, as saying. “He is an important figure in the organization.”

According to reports, when the ISIS fired villages in northern Iraq on Tuesday with mortar shells and Katyusha rockets filled with “poisonous substances” it caused partial choking and skin irritation to more than  40 people.

The Pentagon said last week that they have captured a high-ranking ISIS operative. It is believed that al Bakkar was captured a few weeks ago by the US special forces.