North Korea may have just conducted its fourth nuclear test since 2006. Seismic activity in the country was first detected by monitors in South Korea, which reported a 5.1 magnitude "artificial" earthquake around 9PM ET on Tuesday. Earthquake agencies in other countries noted the abnormalities in the apparent quake that point to a nuclear test — Japan's national meteorological agency said it had a particularly shallow focus point and a strange waveform, while according to the US Geological Survey, the epicenter of the quake occurred near the country's Punggye-ri nuclear test site.
North Korea last conducted a nuclear test in 2013 in an underground site 20 miles west of the town of Hoemun. The move was largely political — North Korea has infamously used its nuclear ambitions as part of its belligerent posture toward its rivals. The country's state television channel appeared to confirm the seismic reports — shortly after the explosion was detected, an announcer said that scientists had successfully detonated a hydrogen bomb. A statement was issued by the Korean Central News Agency, the country's official media agency, soon after.
It's not clear whether the country's claims are accurate — South Korea's intelligence agency has already said the device tested may not have been a hydrogen bomb — but governments around the world have already condemned the possible test. UK foreign secretary Philip Hammond said that an H-bomb test would be a "grave breach" of UN Security Council resolutions, while the US National Security Council said in a statement that it was monitoring the situation, and that it "will not accept [North Korea] as a nuclear state.