(Adds U.S. comment, paragraph 11)

By Louis Charbonneau

UNITED NATIONS, Oct 24 (Reuters) - U.N. Secretary-General Ban Ki-moon urged the world's nuclear powers on Friday to take steps to abolish their atomic arsenals and outlined a set of proposals for eliminating all weapons of mass destruction.

The permanent members of the U.N. Security Council -- the United States, Britain, France, Russia and China -- signed the 1968 nuclear Non-Proliferation Treaty, under which they pledged to negotiate steps on scrapping their nuclear weapons.

While most of the 192 U.N. member states have signed the pact, U.N. officials and signatories without atomic weapons have long complained the five nuclear powers have yet to abandon their warhead stocks.

India, Pakistan and Israel are also widely seen as unofficial members of the nuclear club. North Korea held a nuclear test in 2006 and Western nations believe that Iran is following in Pyongyang's footsteps, a charge Tehran denies.

"Nuclear weapons produce horrific, indiscriminate effects. Even when not used, they pose great risks," Ban told a conference organized by the East-West Institute.

"Accidents could happen any time. The manufacture of nuclear weapons can harm public health and the environment," he said. "Of course, terrorists could acquire nuclear weapons."

While most countries have no plans to obtain atomic weapons, Ban said some still viewed possession of such weapons as a status symbol. He gave no examples.

"Some states view nuclear weapons as offering the ultimate deterrent of nuclear attack, which largely accounts for the estimated 26,000 that still exist," Ban said. He added the world remained concerned about North Korea and Iran.

BAN'S DISARMAMENT PROPOSALS

Arms control experts have also criticized U.S. President George W. Bush's administration for refusing to join the Comprehensive Nuclear Test-Ban Treaty, or CTBT, banning nuclear tests, and launching research on new types of atomic weapons.

They say that sends the wrong signal to countries like Iran and North Korea, which feel threatened by Washington.

A U.S. official who requested anonymity said: "We appreciate the secretary-general's comments, but our policy remains clear. The U.S. does not support the CTBT and will not become a party to it. The U.S. continues to maintain a moratorium on nuclear tests, and urges other states to do likewise."

The Bush administration has declined to submit the treaty for Senate ratification, saying it does not want its options limited by such a pact.

To help end the impasse on disarmament, Ban presented a number of proposals in his speech, including:

- The nuclear weapon states should keep their promises to launch negotiations leading to nuclear disarmament;

- The permanent Security Council members should open discussions on security issues related to disarmament and should try to assure countries without atomic weapons they will never be subjected to a nuclear attack;

- The CTBT should be brought into force and efforts should be made to establish nuclear weapon free zones around the world, including in the Middle East;

- New efforts should be made to eliminate all weapons of mass destruction, including chemical and biological arms, to prevent terrorists from getting WMD and to limit conventional arms production and trade.

Ban also said he supported the idea of the U.N. General Assembly holding a world disarmament summit.

Russia's ambassador to the United States, Sergei Kislyak, told reporters Moscow would need time to study Ban's proposals before reacting to them. (Editing by Peter Cooney)

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