North Korea declared it had successfully conducted a test of a hydrogen bomb, sparking a mix of condemnation and skepticism around the world.
North Korea conducted two tests of a sea-based missile late last year, apparently with mixed results.
South Korea plans to deploy ballistic missiles with increased ranges by 2017, but some experts question whether Seoul can meet that timeline.
China called for the resumption of nuclear negotiations with Pyongyang based on a 2005 agreement to denuclearize North Korea.
North Korea claimed it launched a ballistic missile from a submarine, but some analysts contend it came from a submerged barge.
As the 2015 NPT Review Conference continues in New York, the international community’s failure to halt the spread of nuclear weapons to North Korea looms large.
The United States rejected North Korea’s offer to halt nuclear testing in exchange for a suspension of joint U.S.-South Korean military exercises.
North Korea is prepared to resume negotiations over its nuclear program without preconditions, according to Russia’s foreign minister.
Satellite images suggest that North Korea may have shut down a nuclear reactor that has been a key part of its nuclear weapons program, according to an analysis by a Washington think tank.