A high-ranking U.S. defense official has warned U.S. lawmakers that North Korea is accelerating efforts to deploy missiles capable of threatening the U.S. mainland, U.S. forces deployed in the Asia-Pacific theater and U.S. friends and allies.

In materials submitted to a House subcommittee that convened in Washington on Thursday, Missile Defense Agency director Vice Admiral Jon Hill said North Korea has engaged in a variety of ballistic missiles tests, including launches of mobile and submarine-launched weapons. He also said that North Korea has transferred ballistic missiles and ballistic missile technology to other countries.

Hill warned that potential adversaries of the U.S. are bolstering the number and capabilities of existing missile systems while adding to the capabilities of new missile types, creating an inflection point for U.S. missile defense plans.

In materials submitted to the same subcommittee, U.S. Northern Command and North American Aerospace Defense Command chief Gen. Terrence O’Shaughnessy said North Korea continues to openly threaten the U.S. with intercontinental ballistic missiles(ICBMs) capable of carrying nuclear warheads.

Other U.S. defense officials warned that U.S. security could be threatened if North Korea's ICBM threat outpaces the U.S. deployment of new ground-based interceptors. They added that Pyongyang continues to develop short- and medium-range ballistic missiles to gain political and economic benefits and exert coercive influence on its neighbors.