North Korea ups the stakes

North Korea conducted its sixth and most powerful nuclear test on Sunday, which it said was a successful detonation of an advanced hydrogen bomb, in a dramatic escalation of the isolated state's stand-off with the US and its allies.

The announcement from Pyongyang came a few hours after international seismic agencies detected a man-made earthquake near the North's test site, which Japanese and South Korean officials said was about 10 times more powerful than the tremor picked up after its last test a year ago.

There was no independent confirmation that the detonation was a hydrogen bomb rather than an atomic device.

The test is a direct challenge to US President Donald Trump, who hours earlier had talked by phone to Japanese Prime Minister Shinzo Abe about the "escalating" nuclear crisis in the region and has previously vowed to stop North Korea developing nuclear weapons that could threaten the US.

North Korea, which carries out its nuclear and missile programmes in defiance of UN Security Council resolutions and sanctions, said in an announcement on state television that a hydrogen bomb test ordered by leader Kim Jong-un was a "perfect success" and a "meaningful" step in completing the country's nuclear weapons programmes.

The bomb was designed to be mounted on its newly developed intercontinental ballistic missile, the North said.