NATO head Jens Stoltenberg condemned North Korea's announced hydrogen bomb test Wednesday as a threat to international security and urged Pyongyang to abandon its nuclear weapons programme.

"The nuclear weapons test announced by North Korea undermines regional and international security, and is in clear breach of UN Security Council resolutions," Stoltenberg said in a statement.

"North Korea should abandon nuclear weapons and existing nuclear and ballistic missile programmes in a complete, verifiable and irreversible manner, and engage in credible and authentic talks on denuclearisation," he said.