The 5.3-magnitude earthquake that occurred as a result of the test on Friday indicated the blast was 10 kilotons in yield. If so, it would be the largest ever conducted by the North. The quake was detected near North Korea's Punggye-ri nuclear test site as the country celebrates Foundation Day, marking the anniversary of the founding of the nation in 1948.

North Korean state television announced the "nuclear warhead explosion" in a live broadcast, not long after South Korean President Park Geun-hye blasted North Korean leader Kim Jong Un for the act of "fanatic recklessness." During its broadcast, Pyongyang said it could now mount nuclear warheads on ballistic rockets.

Only several days ago, the country launched three ballistic missiles into the sea as leaders from around the world gathered in China for the G-20 summit. Pyongyang has drawn stern condemnation from the international community over the past several months for its rocket launches, as well for another nuclear test - its fourth - in January. The country's recent belligerence is mainly seen as a response to the US's recent decision to deploy the THAAD anti-missile system to South Korea.

Park also said North Korea had violated UN Security Council resolutions in a direct challenge to the international community. Her office said she has spoken with US President Barack Obama soon afterward during the ASEAN summit in Laos.

Asia on edge

Japan's Prime Minister Shinzo Abe said the suspected nuclear test "could not be tolerated" and that Japan would protest strongly to Pyongyang if confirmed. Foreign Minister Fumio Kishida vowed that if a nuclear test is confirmed, Japan will "lodge a strong protest against North Korea... and immediately respond at the UN Security Council."

US President Barack Obama was briefed about the test on board Air Force One. He said Pyongyang's actions would have "serious consequences" and consulted with leaders in Japan and South Korea, the White House said.

Beijing, one of Pyongyang's only allies, said it "firmly opposes" the test as well, while urging North Korea to refrain from worsening the situation in the region. China's Ministry of Environmental Protection, meanwhile, said it was monitoring radiation levels along its border with the country. Japan said it had also begun to collect air samples.

Pyongyang test-fired three missiles Monday as world powers gathered for a G20 meeting in China, with leader Kim Jong-Un hailing the tests as "perfect", and US President Barack Obama warning it would only up the pressure.

jbh/blc/kl (AFP, AP, Reuters)