Oct 9 (Reuters) - North Korea said on Monday it had safely and successfully carried out an underground nuclear test, flying in the face of a warning from the U.N. Security Council.

The world has five "official" nuclear powers -- the United States, Russia, China, Britain and France.

Following is a summary of the estimated capabilities of declared and undeclared nuclear powers.

OFFICIAL NUCLEAR POWERS:

* UNITED STATES: The United States maintains a sizeable arsenal of nuclear weapons of around 10,000 intact warheads, nearly 6,000 of which are considered active or operational.

-- Approximately 1,700 are deployed on land-based missile systems (Minuteman and Peacekeeper ICBMs).

-- 1,098 on bombers (B-52 and B-2), and 3,168 on submarines.

-- 800 are tactical nuclear weapons (TNWs) and consist of Tomahawk land attack cruise missiles and B61 bombs.

-- According to the May 2002 Treaty of Moscow (the Strategic Offensive Reductions Treaty, or SORT) between the U.S. and the Russian Federation, both are required to reduce their nuclear arsenals to 1,700-2,200 operationally deployed warheads by 2012. * RUSSIA: Russia is estimated to have around 20,000 nuclear weapons. Under the START I Treaty, the Russian nuclear arsenal has been reduced to approximately 7,000 strategic warheads.

* FRANCE: France maintains about 350 nuclear warheads.

* BRITAIN: The UK's stockpile is thought to be less than 200 strategic and "sub-strategic" warheads on nuclear-powered ballistic missile submarines (SSBN).

* CHINA: China maintains an arsenal of about 400 warheads, some 250 "strategic" weapons and some 150 "tactical" weapons. China acceded to the Nuclear Non-Proliferation Treaty (NPT) in 1992 as a nuclear weapon state.

OTHER "DECLARED" NUCLEAR NATIONS:

* NORTH KOREA: On Monday, North Korea conducted its first ever nuclear test. North Korea declared for the first time in 2005 that it had nuclear weapons. North Korea may have enough fissile material for at least eight nuclear weapons, proliferation experts have said.

* INDIA: India has formally declared itself a nuclear weapon state. New Delhi's stock of weapons-grade plutonium is estimated to be between 240-395 kg, which depending on the sophistication of the warhead design, could be used to manufacture 40-90 simple fission weapons.

* PAKISTAN: Last July, reports said that Pakistan was building a new nuclear reactor that could produce enough plutonium for 40 to 50 nuclear weapons a year in an expansion of its nuclear programme. Pakistan is not a signatory to NPT.

OTHER UNDECLARED NATIONS:

* ISRAEL: Based on estimates of the plutonium production capacity of the Dimona reactor, where the programme is based, Israel has approximately 100-200 nuclear explosive devices. Israel has not signed the NPT treaty.

* IRAN: Despite months of talks, Tehran has made no commitment to suspend the uranium enrichment process the West fears it is using as a step towards building atomic bombs.

Sources: Reuters/www.nti.org (Nuclear Threat Initiative)

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