Four Islamic State (ISIS) leaders have been killed over the past three weeks, according to the latest Pentagon briefing.

Army Col. Ryan Dillon, a spokesman for Operation Inherent Resolve, told reporters in a press briefing Tuesday the names of the four ISIS leaders “hunted down” by U.S. aircraft.

The militants killed include those responsible for plotting terrorist attacks abroad, obtaining weapons for ISIS, and keeping up the propaganda arm of the terrorist group.

U.S. Central Command released a statement with the following information about the dead militants:

“The removal of these key terrorists disrupts ISIS’ weapons engineering activities and their ability to recruit and train terrorists. It also reduces their ability to plan and conduct terrorist attacks both within Syria and Iraq, and abroad,” the statement continued.

The U.S. fight against ISIS has been successful in recent months as the terrorist group lost control over its largest city and capital, Mosul, to Iraqi forces.

Dillon warned, however, that even though the caliphate continues to fall apart, ISIS continues to pose a major threat to U.S. national security.