WASHINGTON -- US Defense Secretary Jim Mattis vowed Tuesday to bolster the defense of Guam against North Korea's ballistic missile threats.

At a congressional hearing, Mattis was asked by Guam Delegate Madeleine Bordello whether the US territory in the Western Pacific is adequately defended from "theater missile threats" and how he plans to strengthen the defense systems already in place.

"We will continue bolstering them to keep pace with the threat out of North Korea," the secretary said. Bordello had noted the presence of the THAAD missile defense system on her island, as well as B-2 and B-52 bombers. Guam is also home to a major US Air Force base.

"Besides the THAAD system we also keep the Aegis Ballistic Missile Defense US Navy warship in the waters out there. We can always reinforce that," Mattis said. "We also have several of those ships in Japanese waters right now and they can move back and forth to include coverage of Guam in the mobile way that comes to our Navy."