FACTBOX-What is the Non-Proliferation Treaty?

(Reuters) - U.S. President Barack Obama will hold a summit with Russian leaders in Moscow next week seeking to "reset" relations that had hit a post-Cold War low under his predecessor.

In April, Russian President Dmitry Medvedev and Obama agreed to pursue a new arms deal, in accordance with U.S. and Russian obligations in the nuclear Non-Proliferation Treaty (NPT).

Here are some key facts about the treaty:

* 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 Soviet Union). The five are the permanent members of the U.N. Security Council.

* SIGNATORIES:

-- A total of 189 countries are party to the NPT. 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.