A suburban Cincinnati man accused of plotting to attack the U.S. Capitol in support of Islamic State extremists is due back in federal court.

An indictment last week added a fourth charge against 21-year-old Christopher Lee Cornell. The count of attempting to provide material support to a U.S.-designated foreign terrorist organization carries a potential sentence of up to 15 years in prison with conviction.

He already faced two charges with possible 20-year sentences. Cornell pleaded not guilty to those charges.

He is scheduled for arraignment Tuesday in Cincinnati on the new count. He has been held without bond since his Jan. 14 arrest.

His father has said Cornell was coerced by a government "snitch."

U.S. authorities are on alert for "lone wolf" terrorist plots inspired by the Islamic State group.