A northern Virginia man arrested in a sting operation has pleaded guilty to trying to help the Islamic State group, and faces up to 20 years in prison.

Twenty-five-year-old Haris Qamar (keh-MARR') of Burke admitted in federal court in Alexandria on Monday that he used the handle "newerajihadi" on Twitter to promote the Islamic State.

Prosecutors say Qamar worked with a government informant to film and photograph landmarks in the D.C. region, including the Pentagon, for use in propaganda videos to encourage lone-wolf attacks.

After Monday's hearing, Qamar's father said his son lost touch with reality as he adopted the online persona of an Islamic radical.