U.S. President Barack Obama has condemned North Korea's fifth nuclear test in the strongest possible terms and warned to take additional significant steps including new sanctions.

The U.S. leader also said his country will never accept North Korea as a nuclear state and reaffirmed Washington's security commitment to South Korea.

In a statement issued on Friday, Obama said the North's nuclear test is a grave threat to regional security and international peace and stability. He said that North Korea stands out as the only country to have tested nuclear weapons this century.

While calling the nuclear experiment a flagrant violation of multiple UN Security Council resolutions, he said it makes clear North Korea's disregard for international norms and standards for behavior, and demonstrates it has no interest in being a responsible member of the international community.

He also vowed to work with the international community to "take additional significant steps including new sanctions to demonstrate to North Korea that there are consequences to its unlawful and dangerous actions."

Obama also mentioned an unshakeable U.S. commitment to defending its allies in the region including through the deployment of the THAAD battery to South Korea and the duty to provide extended deterrence.

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