After weeks of speculation, North Korea appears to have fulfilled its pledge to conduct a third nuclear weapon test. According to the North's official news agency, an underground nuclear explosion was carried out in a tunnel at the Punggye-ri test site in the north-east of the country.
North Korea previously conducted two nuclear tests at the site (in 2006 and in 2009), although the first test was widely viewed as a failure.
The latest SIPRI expert comment by SIPRI Senior Researcher Shannon Kile addresses questions on technical details of the recent tests.