North Korea threatened to use nukes to retaliate against the United States if Washington policymakers continue to blackmail Pyongyang with nuclear weapons, the North's state media said Tuesday.

North Korea's Institute of International Studies on Monday unveiled a memorandum exposing what it called Washington's nuclear crimes, according to the Korean Central News Agency.

It said the criminal nature of Washington's nuclear policy can be most evidently found in its stance toward North Korea.

"As long as the US exists on the earth, a world without nuclear weapons is no more than a daydream and our planet will be in peace only when it is free from its aggression," the institute was quoted as saying by the KCNA.

North Korea conducted its fifth and most powerful nuclear test on Sept. 9, eight months after its fourth nuke detonation.

Pyongyang after its latest test claimed it successfully conducted a warhead explosion test, raising concerns the North may be moving closer to developing a nuclear-tipped intercontinental ballistic missile that can fly as far as the US mainland.

Last week, the US sent two supersonic B-1B Lancer bombers to the skies over South Korea in a show of force against North Korea.

In an apparent protest against Washington's move, North Korea has said that it will beef up its nuclear force by sticking to its nuclear and missile programs.

"The more the US increases its nuclear blackmail, the more we will strengthen our iron-fist of nukes by hundreds of thousands of times," the KCNA said. (Yonhap)