FACTBOX-Key facts about the Nuclear Non-Proliferation Treaty

(Reuters) - U.N. Secretary-General Ban Ki-moon said on Monday the nuclear Non-Proliferation Treaty was suffering a crisis of confidence as member states meet to mull how to prevent the pact from falling apart.

Representatives from 189 nations are holding a Preparatory Committee session in Vienna until May 11 to smooth a path to the next full conference in 2010. But memories are strong of stalemate hit at the last NPT Review Conference in 2005.

Here are some key facts about the treaty, regarded as the cornerstone of global efforts to prevent the proliferation of nuclear weapons:

PURPOSE OF THE NPT

-- The objective of the treaty, which took effect in 1970, is to halt the spread of nuclear weapons-making capability, guarantee the right of all members to develop nuclear energy for peaceful ends and -- for the original five nuclear weapons powers -- to phase out their arsenals.

-- The treaty defines nuclear-armed states as those that "manufactured and exploded a nuclear weapon or other nuclear device prior to January 1, 1967". They are the United States, Britain, France, China and Russia (which assumed rights and obligations from the then-Soviet Union). The five are the permanent members of the United Nations Security Council.

SIGNATORIES

-- A total of 189 nations are party to the NPT. North Korea dropped out in 2003. Nuclear states are bound not to transfer nuclear weapons or to help non-nuclear states obtain them.

South Africa signed the treaty in 1991 and admitted producing nuclear devices until 1970.