North Korea said today it had carried out a "successful" hydrogen bomb test -- its fourth nuclear blast -- rattling the region with its latest bout of sabre rattling.
Here are five questions about North Korea's nuclear programme and its impact on regional diplomacy and security:
Q: Can North Korea's claim be believed?
A. Experts broadly agree that the country probably carried out some kind of nuclear explosion but are sceptical over the "hydrogen" assertion.
The first clue that something happened came with reports of a 5.1 magnitude earthquake near the North's nuclear test facility. North Korean state television later announced that it was a hydrogen bomb test.
But Australian nuclear policy and arms control specialist Crispin Rovere said that "the seismic data that's been received indicates that the explosion is probably significantly below what one would expect from an H-bomb test".
"So initially it seems to be that they've successfully conducted a nuclear test but unsuccessfully completed the second-stage hydrogen explosion."
Q. What does the new test mean in terms of North Korea's nuclear development?
A. Despite doubts over the claim it was a hydrogen bomb, it still demonstrates the country's commitment to carrying on with its nuclear programme.
It comes after three previous nuclear explosions between 2006 and 2013 and a boast last year the regime had developed a hydrogen bomb.
North Korea is continuing with their test programme without regard to what the world thinks, Christopher Hill, former US chief negotiator to the six-party talks aimed at the North's denuclearisation, told the BBC.
"We have a big problem regardless of how large the explosion was today," Hill said.
Q. What does the test mean for international relations and diplomacy in Northeast Asia?
A. Most of all, it will mark a new low point in relations between North Korea and neighbouring China, which has been the country's main diplomatic supporter for decades.
Beijing's patience has run increasingly thin as it strongly opposes Pyongyang's nuclear development and sees it as a factor for instability on the Korean peninsula, where it has strong trade relations with North Korean rival South Korea.
"Beijing will face increased pressure both domestically and internationally to punish and rein in Kim Jong-Un and to ultimately force Pyongyang to give up its nuclear weapons," said Yanmei Xie, International Crisis Group's Senior Analyst of Northeast Asia based in Beijing.
"But there is likely to be a repeat of the worn playbook of denunciation, tightening of sanctions, and calling for resurrection of the six party talks."
Relations with South Korea are also likely to suffer, with attempts to improve dialogue and reduce tensions along their heavily fortified border to come under renewed pressure. Japan, a target of previous North Korean threats, is likely to increase its guard.
Q. Why now?
A. Kim, who has carried out numerous purges of senior officials since coming to power after the death of his father Kim Jong-Il in December 2011, is believed to constantly need to solidify his power base and demonstrate achievements even greater than those of his father and grandfather, North Korea's founder Kim Il-Sung.
The announcement also comes just two days before his January 8 birthday and also in advance of an expected congress of North Korea's ruling Workers' Party -- the first such gathering in 35 years.
"The purpose of this is firstly to display to the world that it has acquired a new technology as to the nuclear weapons programme," said Toshimitsu Shigemura, a professor at Waseda University in Tokyo and an expert on North Korea.
"Secondly, with the (claimed) development of hydrogen nuclear weapons, Kim Jong-Un now has a 'great achievement' that even Kim Il-Sung or Kim Jong-Il could not realise."
Q. What's next?
A. Past North Korean nuclear and ballistic missile tests have been followed by condemnatory United Nations Security Council resolutions and additional sanctions.
Diplomats said that the UN Security Council is to hold an emergency meeting on North Korea on Wednesday.
"This clearly violates UN Security Council resolutions and is a grave challenge against international efforts for non-proliferation," said Japanese Prime Minister Shinzo Abe.