The group, of two 16-year-old and 17-year-old girls and a 16-year-old boy, were considering targeting a church, synagogue, or police station.
The assassination is certainly an important development and illustrates how important the US support for Iraq and the war on ISIS continues to be.
Khadijah was also considered the group's Chief of Global Operations in Iraq.
The Taiba resident, 21-year-old Kamal Nashaf, also pledged allegiance to ISIS, the agencies noted.
As long as terrorist groups exploit illicit trade networks, the risk of their expansion into North Africa and Europe remains dangerously high.
The man was said to have used his knowledge of technology to send instructional videos to ISIS members on how to hack computers, steal credit card information and construct fake documents.
Sharifullah is expected to appear in the Eastern District of Virginia later today, and, if convicted, faces a maximum penalty of life in prison.
Abdisatar Ahmed Hassan, from Minneapolis, was accused of joining ISIS by travelling to Somalia from his home state on two separate occasions.
The attack took place in the Fronhof, a market square in the western German city where live bands were playing as part of a festival marking its 650th anniversary.
Thursday's call from PKK leader Abdullah Ocalan for the group to disarm and disband could potentially lead to ending a 40-year conflict.