U.S. intelligence officials are warning about the growing use of encrypted communication and private messaging by supporters of the Islamic State.

The officials told a House committee on Wednesday that such modes of communications are complicating law enforcement efforts to keep tabs on extremists and terror suspects.

John Mulligan, the deputy director of the National Counterterrorism Center, said in his prepared remarks that one of the two men involved in an attempted terror attack in Garland, Texas urged fellow Islamic State supporters before the shooting to move their communications to private Twitter messages.

Michael Steinbach, the head of the FBI's counterterrorism division, said changing technology is outpacing laws that allow the FBI to intercept communications.