FACTBOX: What is the Non-Proliferation Treaty?

(Reuters) - A senior Iranian official suggested on Monday Iran should quit a treaty designed to stop the spread of nuclear weapons in protest at U.N. censure of its nuclear activity, but its atomic energy chief dismissed such a move.

Here are some key facts about the Non-Proliferation Treaty

(NPT).

* 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.

* NON-SIGNATORIES:

-- Two non-signatories, India and Pakistan, developed nuclear arsenals and another, Israel, is widely assumed to have one but has never confirmed it publicly.

* IRAN:

-- Iran has been a non-nuclear-weapon state party to the NPT since 1970. It has a uranium enrichment program which it says is geared to providing energy so it can export more oil and gas. Western powers suspect Iran's underlying agenda is to develop the means to make atomic bombs because of its past failure to declare nuclear facilities to the IAEA and continued restrictions on U.N. inspections. Iran is under U.N. sanctions for refusing to suspend the disputed activity. Iran on Sunday announced plans to build 10 more nuclear sites in a swipe at growing pressure to rein in its atomic work.

* NORTH KOREA:

-- North Korea signed in 1985 but left in 2003 after U.S. officials confronted it with evidence they said pointed to a covert enrichment program. Pyongyang also expelled inspectors from the International Atomic Energy Agency (IAEA).

-- North Korea claimed it had conducted a nuclear test on May 25, its second since 2006 and a move that was swiftly condemned worldwide and resulted in punitive measures against Pyongyang. Last month Obama renewed sanctions against North Korea, declaring that its nuclear program posed a national security risk to the United States and a danger to the Korean Peninsula. The United Nations Security Council also expanded U.N. sanctions with a ban on all weapons exports from North Korea and most arms imports.

-- The United States said it had cracked down on companies involved in North Korea's suspected missile proliferation and in purchases of equipment that could be used in a nuclear weapons program.

* TREATY TRADEOFF:

-- Non-nuclear signatories must not develop or acquire such weapons but are given an assurance of assistance in developing nuclear energy for peaceful purposes, monitored by inspectors from the Vienna-based IAEA.

* ESCAPE CLAUSE:

-- The treaty is divided into 11 articles, including one that enables a state to withdraw "if it decides that extraordinary events ... have jeopardized the supreme interests of its country." A state must give three months' notice to other treaty parties and the U.N. Security Council.

* INDEFINITE EXTENSION:

-- At the 1995 review conference, the treaty was extended indefinitely at the behest of nuclear weapons powers. Developing countries agreed to the extension after a commitment from weapons states to step up disarmament, ease access to nuclear energy for development and seek a nuclear weapons-free zone in the Middle East. They say these pledges have not been fully