The NPT, opened for signature in 1968, recognises five nuclear-armed states, the US, Russia, China, France and UK, and requires them to work toward disarmament. All other signatories, including Iran, commit to not developing nuclear weapons. In return, every member is permitted to pursue civilian nuclear energy under the watch of the International Atomic Energy Agency, the UN's nuclear watchdog. The treaty also contains a withdrawal clause, allowing any member to exit with just three months' notice if it believes extraordinary circumstances threaten its national security.