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The world's nuclear arsenal

Yet it is more than 30 years since they signed the Nuclear Non-Proliferation Treaty (NPT), which includes a commitment to dismantle these weapons.

In the intervening period, the Cold War has ended but new nuclear threats have emerged.

Nuclear disarmament

The Nuclear Non-Proliferation Treaty, signed in 1970, is the most widely accepted arms control agreement.

A total of 187 states have now signed the agreement, with exceptions being Cuba, Israel, India, and Pakistan.

The treaty obliges the nuclear powers never to transfer their nuclear technology to other countries, and forbids other countries from acquiring nuclear capability.

In turn, the nuclear powers are supposed to work towards the elimination of their stockpiles.

The nuclear power club

There are five countries who have admitted to having nuclear weapons and signed the NPT and the Comprehensive Test Ban Treaty (CTBT), which bans nuclear test explosions.

• United States Set off first nuclear blast in 1945. Conducted over 1,030 tests. Arsenal of about 12,070 warheads. Missile range of 8,100 miles.

• Russia First test in 1949. Conducted 715 tests in total. Arsenal of about 28,240 warheads - but an estimated 18,000 of these are awaiting dismantlement or in reserve. Missile range of 6,800 miles

• Britain First test in 1952. Conducted 45 tests in total. Arsenal of about 400 warheads. Missile range of 7,500 miles.

• France First test in 1960. Arsenal of about 510 warheads. Missile range of 3,300 miles.

• China First test in 1964. Conducted 45 tests, and helped Pakistan develop its nuclear capabilities. Arsenal of about 425 warheads. Missile range of 6,800 miles.

New nuclear states

India and Pakistan both exploded nuclear devices in 1998, openly declaring themselves to be nuclear powers.

Unlike the other nuclear powers, neither country has signed the CTBT or the NPT, and they are therefore not considered to be official nuclear states by the original five nuclear powers.

• India First tested a "peaceful nuclear explosive device" in May 1974, and claimed its nuclear programme was for peaceful purposes only. Two subsequent tests in May 1998. Estimates of its nuclear arsenal vary from 60 to 250 warheads. It's missile range is between 1,500 to 2,000 miles.

• Pakistan Two tests in May 1998. As with India, no-one knows exactly how many warheads it has. It is thought to be somewhere between 10 and 15, but could be as many as 150. Missile range between 1,500 to 1,800 miles.

• Israel Known to have nuclear weapons capability, but has never declared it or tested. It has an estimated arsenal of 100 warheads and a missile range of 940 miles.

Suspected nuclear aspirants

These countries have all signed the NPT, but they are nevertheless suspected of secretly trying to develop their own nuclear arsenals.

• North Korea Suspected of developing a nuclear bomb, and might have two warheads. Activity at its Yongbyon nuclear research centre was frozen under 1994 agreement with the US. Its missile range is 600 to 900 miles.

• Iran Suspected of being within 5 to 10 years of producing a nuclear bomb. Seeking to recruit Russian nuclear scientists. Missile range 310 miles.

• Iraq Before Gulf War was two years from producing bomb. United Nations weapons inspectors have not visited Iraq since UNSCOM withdrew in December 1998. Missile range up to 470 miles.

• Libya Despite numerous attempts to obtain nuclear weapons and technology, is thought to have made little progress. Missile range 190 miles.