North Korea claimed to have conducted its first nuclear test on 9 October 2006; however seismic recordings revealed the underground blast to be relatively small.
The reclusive Stalinist state has previously declared that it has nuclear weapons and is building more, though the outside world is not certain how many it actually possesses.
The US analyst group Global Security suggests that North Korea could have enough reprocessed plutonium for up to eight bombs. American intelligence estimates vary from 1-2 bombs to around 15 warheads. Many experts believe North Korea has also attempted to enrich uranium for nuclear weapons.
North Korea withdrew from the NPT treaty in October 2002 and has refused to allow the International Atomic Energy Agency (IAEA) to inspect its facilities.
It has also pursued an ambitious missile building programme. The long-range Taepodong I missile, tested in 1998, is thought to have a range of about 2,000km. However it is not known whether it has the technology required to fit any of its missiles with a nuclear warhead.