North Korea's "reckless pursuit of nuclear weapons" demands a "united response" from the international community, NATO said on Wednesday.
Pyongyang's nuclear program is in "violation of multiple UN Security Council resolutions and a major threat to the non-proliferation regime," NATO said in a statement.
Meanwhile, speaking at a news conference at a military base in Tapa, Estonia, the organization's Secretary General Jens Stoltenberg called on North Korea to "abandon all nuclear and ballistic missile programs".
The reclusive regime on Sunday claimed to have detonated a new hydrogen bomb, confirming suspicions about the communist state's sixth-ever nuclear test.
Pyongyang's official KCNA news agency said that the "perfect" test involved a hydrogen bomb which could be mounted on an intercontinental ballistic missile (ICBM).
North Korea is barred from testing nuclear and ballistic missiles, and was recently hit with strengthened UN Security Council sanctions for launching a pair of ICBMs in July.
The UN in early August imposed new sanctions on Pyongyang with a sweeping ban on exports of coal, iron, lead and seafood that could eliminate $1 billion in the country's annual revenues.
