North Korea has said it has tested a miniaturised hydrogen bomb.
Suspicion of an underground test was first raised after the US Geological Survey said the epicentre of the quake – detected at 10:00 Pyongyang time (01:30 GMT) – was in the north-east of the country, some 50km (30 miles) from Kilju city, near Punggye-ri.
Then in a surprise announcement, a newsreader on North Korean state TV said: “The republic’s first hydrogen bomb test has been successfully performed at 10:00 am on January 6, 2016.”
It could be days or weeks before independent tests are able to verify the claim.
Last month, North Korean leader Kim Jong-un said Pyongyang had developed a hydrogen bomb, although many experts were sceptical.