North Korea's "increasingly sophisticated" nuclear weapons and missile programs threaten the United States and its allies, the U.S. Department of Defense said in a new report published on Monday outlining Washington's "rationale" for possessing its own nuclear arsenal.

The statement comes after the DPRK conducted four rounds of missile tests in March -- its most ever in a one-month span -- and also follows Secretary of State Pompeo's recent call for the world to "remain united" in enforcing sanctions against the North, as punishment for its various weapons programs.