The ISIS figure captured by American Special Operations forces in Iraq a few weeks ago was the terror group’s chief of its chemical weapons unit, a U.S. official said today.

ISIS has a rudimentary mustard gas capability that it used last summer to limited effect against Kurdish forces in Iraq and Syria, U.S. officials said. It is believed that ISIS has sought to improve its capability to broaden its use in Iraq and Syria.

The individual captured by the new Iraq-based Expeditionary Targeting Force (ETF) was in charge of the unit developing chemical weapons for ISIS, a U.S. official told ABC News.

Iraqi officials have identified him as Sleiman Daoud al-Afari, who used to work for the organization set up by Saddam Hussein to develop chemical weapons for his regime, according to the Associated Press.