Background: The nuclear nations

[NNN0LHI]

http://www.guardian.co.uk/world/2009/apr/05/nuclear-weapons-non-proliferation

Sunday 5 April 2009 13.23 BST

North Korea, along with India, Pakistan and Israel, is one of four countries not to have signed the nuclear non-proliferation treaty

The US president, Barack Obama, wants to strengthen the world's nuclear non-proliferation regime, based on the 1968 nuclear non-proliferation treaty (NPT).

The treaty is the bedrock of attempts to prevent the spread of nuclear weapons, but is fraying at the edges.

All five permanent members of the UN security council – the US, Russia, China, France and Britain – are nuclear powers, and are recognised as such in the NPT.

The idea at the heart of the treaty is that the five are to progressively disarm in return for other states not acquiring the bomb.