U.S. Secretary of State John Kerry says he is deeply concerned about North Korea after the communist government announced that it had conducted its fifth nuclear test.
A fifth test, North Korea's most powerful nuclear experiment so far, is believed to have been carried out overnight at the country's northeastern nuclear test site.
"If we put that into perspective, it is smaller than Hiroshima or Nagasaki, but would still be capable of ripping the heart out of a city", said Karl Dewey, an analyst at IHS Janes.
North Korea's state TV says Friday's nuclear test "examined and confirmed" specific features of a nuclear warhead created to be mounted on ballistic missiles.
South Korean monitors said Friday's nuclear test had a yield equivalent to 10 kilotons of TNT, which would make it North Korea's most powerful of five tests to date.
Christopher Hill, the former United States ambassador to South Korea, said Friday it's time to stop guessing about North Korea's capabilities and start planning a response. But numerous rounds of sanctions so far only have seemed to strengthen Kim Jong Un's resolve to show off his military might. The first was staged in October 2006, followed by the second in May 2009 and the third in February 2013.
Japan's Foreign Minister Fumio Kishida also confirmed that Japan Meteorological Agency has detected shaking patterns that are not from a naturally occurred quake.
Two members of the ruling Saenuri Party and the main opposition Minjoo Party, who attended the briefing, told reporters that the NIS head expressed concerns about the country's significantly faster-than-expected speed at developing a miniaturized nuclear warhead.
If Pyongyang can make a nuclear device small enough to fit on a warhead, and can bolster the range and accuracy of its missiles, it might one day achieve its oft-stated aim of hitting United States targets. But its claims to that in the past have been discounted. "Secondly, there could be additional names added to the existing sanctions regime, so further designations, and thirdly, there could be a tightening up and a strengthening of the sanctions regime", he said.
It is unusual for Ban to call a press conference to condemn North Korean provocations, rather than issuing a statement.
Among Pyongyang's regular demands are for Washington to withdraw its troops from the region and to sign a peace treaty formally ending the Korean War.
Outside experts said authenticating North Korea's claim to have mastered miniaturisation would be hard using seismic data alone.
"Nobody wants to see that". Not only has the range of the weapons successfully tested jumped significantly, but the country is working to ideal new platforms for launching them - submarines and mobile launchers.
North Korea is now subject to a number of global sanctions regimes, including five sanctions resolutions from the Security Council.
That blast came just days after North Korea test-fired three ballistic missiles, which landed in Japan's Air Defense Identification Zone, about 155 miles (250 kilometers) from a Japanese island.
This week's events are yet another slap in the face for Pyongyang's chief ally, China, which has been under pressure to rein in its increasingly embarrassing neighbour. "We must strongly protest against it", Abe said, adding that Japan would liaise closely on the matter with the United States and South Korea.
They also agreed to have a more "in-depth" discussion on the North's latest nuclear test and its ramifications when they meet in Seoul on Tuesday next week, it added. "They aren't a backwards state any more", Lewis said.
The intelligence agency in the South said that is an indicator of rapid advancement in the North's nuclear technology, according to a lawmaker briefed by the agency Friday.
This test follows the January detonation of a device the North claimed was a hydrogen bomb, which led to wide condemnation and tougher worldwide sanctions. Politically, there is a good chance that any negotiations close on the heels of a nuclear test would be interpreted as a successful case of "nuclear blackmail".