Facts about the nuclear nonproliferation treaty:

--Countries that have nuclear weapons will not help other countries obtain or develop them. Non-weapon states agree not to try to get nuclear arms.

--Countries with nuclear weapons will negotiate for nuclear disarmament.

--Countries without nuclear weapons will allow the International Atomic Energy Agency to oversee their nuclear facilities.

--Countries will exchange peaceful nuclear technology.

--Entered into force in 1970; signed by 187 countries. Extended indefinitely in 1995.

--India, Pakistan, Israel and Cuba are the only countries that haven't signed on. Cuba is a member of a treaty establishing a nuclear-free zone in Latin America.