El Shafee Elsheikh and Alexanda Kotey are two of four men who were dubbed “the Beatles” by the hostages because of the captors' British accents.
The charges are a milestone in a yearslong effort by U.S. authorities to bring to justice members of the group known for beheadings and barbaric treatment of aid workers, journalists and other hostages in Syria.
“If you have American blood in your veins or American blood on your hands, you will face American justice,” said Demers, the department's top national security official.
The indictment charges the men in connection with the deaths of four American hostages — Foley, journalist Steven Sotloff and aid workers Peter Kassig and Kayla Mueller — as well as European and Japanese nationals who were also held captive.
In July 2014, according to the indictment, Elsheikh described to a family member his participation in an IS attack on the Syrian Army.