North Korea has called U.S. National Security Adviser John Bolton a "war monger" and "defective human product" after he called the North's recent tests of short-range missile a violation of U.N. Security Council resolutions.

Pyongyang's official Korean Central News Agency on Monday carried a statement by an unnamed spokesman of North Korea's Foreign Ministry who said that Pyongyang was rightfully exercising its rights to self-defense with the launches.

North Korea tested short-range ballistic missiles on May 4 and May 9, ending a pause in launches that began in late 2017.

The tests have been seen as a way for North Korea to pressure Washington to soften its stance on easing sanctions against it without actually causing the negotiations to collapse.