PYONGYANG/SEOUL: North Korea said it has hit the button on its fifth and potentially most powerful nuclear test Friday morning, claiming to have successfully detonated a nuclear warhead that could be mounted on ballistic rockets. Seismic activity was detected Friday morning near Punggye-ri – the same location as four other tests. The US Geological Survey reported a 5.3-magnitude earthquake but later termed it an explosion. “We are currently analysing whether it was a successful test,” a South Korean National Defence Ministry official told CNN. A US official told CNN that it looked like a nuclear test but confirmation would be dependent on seismic readings, location of the seismic event and whether it can be matched to an underground test site. The blast, detected around 9am, local time (8.30pm ET), is estimated to have had the explosive power of 10 kilotons, almost twice as large as North Korea’s most recent test in January, said Kim Nam-wook of South Korea’s Meteorological Administration. The test comes on North Korea’s national day, and six months after it claimed it had miniaturised nuclear warheads to fit on ballistic missiles. At the same time, South Korea is negotiating an expected deployment of a US missile defence system, a plan that Pyonyang has decried as provocative. “It’s hard for us to verify their claim. My deep fear is that they will launch a live nuclear weapon on one of their missiles, but that would be extremely dangerous as that could trigger a war,” said Melissa Hanham, a senior research associate at the James Centre for Non-proliferation Studies. World leaders condemned the test, saying it was a clear violation of the UN Security Council resolutions and the Security Council plans to hold an emergency meeting on the issue Friday. President Barack Obama has also warned North Korea that it would face consequences to its unlawful and dangerous actions. He said he spoke to the leaders of South Korea and Japan by phone and that all three agreed to take additional significant steps including new sanctions. “To be clear, the United States does not, and never will, accept North Korea as a nuclear state,” a statement quoted Obama as saying. South Korean President Park Geun-hye called Kim Jong Un’s regime “fanatically reckless”. “The only thing that (the) Kim Jong Un regime can gain from the nuclear tests is stronger sanctions from the international community and its isolation. Such provocation will eventually hasten its path to self-destruction,” she said in a statement. “South Korea worries that Pyongyang is progressing towards its goal of mounting a nuclear warhead to ballistic missiles,” a South Korean lawmaker told reporters Friday. Japanese Prime Minister Shinzo Abe told reporters Friday that it was “absolutely unacceptable” if North Korea had conducted another nuclear test. Obama, who just returned from Asia, called the test a grave threat to international security. He said he reaffirmed to Park and Abe the “unshakeable US commitment to take necessary steps to defend our allies in the region” including through the planned deployment of the Terminal High Altitude Area Defence, or THAAD, anti-missile system in South Korea. In addition to January’s nuclear test, North Korea has tested a number of ballistic missiles, including some launched from a submarine last month and three more launched from land this week. Previous Security Council resolutions prohibit North Korea from conducting nuclear tests and launching ballistic missiles. After North Korea’s test in January, the council imposed a round of sanctions two months later. The sanctions included banning Pyongyang from exporting most of its natural resources, prohibiting the supply of aviation fuel and the sale of small arms to North Korea and requiring the inspection of all North Korean planes and ships carrying cargo abroad.