Q&A: What is the CTBT?

The Comprehensive Test Ban Treaty (CTBT) is one of the most complex treaties ever written - and its ratification is proving just as testing.

If it comes into force, it will mean that all nuclear explosions anywhere in the world are banned. Air-burst detonations are already covered by an earlier agreement, the Partial Test Ban Treaty.

The CTBT sets out nuclear disarmament as a goal but diplomatically avoids the politics of the issue.

Its supporters argue that while the aim of the treaty remains total nuclear disarmament, the CTBT is capable of preventing the development of new weapons, or improvement of those that already exist.

Former US President Dwight Eisenhower was among the first to propose the treaty, in the 1950s, and while he actively built up nuclear stockpiles, he said his failure to successfully clinch a deal was the "greatest disappointment" of his administration.

After decades of false starts, the traditional "big five" nuclear powers of the USA, Russia, China, the UK and France backed talks which led to the CTBT being created at the United Nations in September 1996.

President Bill Clinton was the first world leader to sign the historic document. To date 159 states have followed.

So how does it work?

Once ratification is completed, the Vienna-based test ban organisation will report if it believes an explosion has taken place.

This work will be carried out by 321 monitoring stations and 16 laboratories throughout the world.

The scientists will be able to demand the right to inspect an area if they believe a nuclear test has been carried out.

So the CTBT has been an international success?

Not yet.

The treaty cannot come into force until 44 individually-named states ratify it in their own legislatures.

The CTBT names the 44 states known or believed to have nuclear reactors capable of making material needed for a nuclear bomb.

To date, 30 of this group have ratified, including three of the big five, the UK, France and Russia.

Among other significant nuclear states yet to ratify are Israel, Pakistan and India. Israel - which does not formally admit to having nuclear weapons but is widely believed to have them - signed the treaty in 1996.

But surely everyone must want to sign?

While almost every nation subscribes to the test ban treaty's noble aims, the realities of international power politics are playing their part with many nations seemingly waiting to see what the US does.

President Bill Clinton has warned Congress that if it fails to ratify the treaty it would "be a signal that the United States wants to lead the world away from the cause of non-proliferation".

He says that the US now has the technology to safely stockpile weapons, carry out computer simulated tests and monitor other states, leaving it with no excuse not to sign.

Congress rejected the legislation on 13 October 1999, after Republicans argued that the CTBT would fail to properly monitor other nations.

What's holding it up?

Many nations say a test ban without disarmament is no longer good enough.

Both India and Pakistan, which carried out tit-for-tat nuclear tests in 1998, remain opposed to the CTBT, though they have faced massive US pressure to sign.

India has publicly argued that the CTBT merely formalises nuclear discrimination, allowing the big five to maintain modern weapons but preventing others from developing an adequate nuclear deterrent.

Another argument against ratification is that the US also remains capable of breaking the spirit of the treaty by continuing with research into ballistic missile defences, the successor to former US President Ronald Reagan's "Star Wars" programme.

Are other talks taking place?

Large scale disarmament talks are currently failing to bear fruit.

Talks at the Conference on Disarmament in Geneva have been frequently criticised as flawed and bogged down in procedural wrangling.

The conference president said that its work could only be a "microcosm" of the wider international environment which has seen nuclear tension rise in the past 18 months.

The Canberra Commission of 1997, a side report linked to the Conference on Disarmament, argued that if states carried out a number of measures including taking weapons off alert and mothballing some technologies, countries would feel able to negotiate.

What about talks between Russia and the US?

Opening sessions of the "Start III" (Strategic Arms Reduction) negotiations between the US and Russia have yet to get off the ground even though they hold out the prospect of reducing the number of warheads held by each nation to as low as 1,000.

Moscow has also warned the US that its missile defence projects, which could only go ahead under a modification of the key 1972 Anti-Ballistic Missile treaty, could spark an entirely new and far more dangerous arms race.