After explicit threats to the U.S. territory of Guam by North Korea last year, Secretary of Defense Jim Mattis promised to reinforce the island’s defense Tuesday.

“We will continue bolstering [defense] to keep pace with the threat out of North Korea,” said Mattis in a House Armed Service Committee hearing.

The statement came in response to a question from Madeleine Bordallo, Guam’s delegate to the House about Guam’s vulnerability to “theater missile threats.” Last year in reaction to President Donald Trump threatening North Korea with “fire and fury,” the country threatened to “bracket” Guam with ballistic missiles. North Korea’s threat meant that they would test-fire ballistic missiles that would fall into the ocean all around the island. Despite creating a video previewing the missile tests, North Korea never followed through with the threat.

Guam is home to two critical U.S. military bases, U.S. Naval Base Guam and Andersen Air Force Base. The island houses U.S. bombers that can be equipped with nuclear weapons.

In 2013 a Terminal High Altitude Area Defense (THAAD) system was installed on the island to defend it from ballistic missiles.

“Besides the THAAD system we also keep the Aegis Ballistic Missile Defense U.S. Navy warship in the waters out there. We can always reinforce that,” said Mattis  “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.”

The Aegis system is designed to shoot down short and intermediate range ballistic missiles. Mattis said that the Defense Department would also consider adding a land version of the Aegis system in the future.

Guam’s bases are the closest military installations on U.S. soil to North Korea, only around 2,100 miles away. Last year North Korea demonstrated the theoretical ability to hit targets much farther than that, anywhere in the continental U.S. through a November intercontinental ballistic missile test.