Minutes of a Pentagon meeting to prepare for a conference on a new generation of nuclear weapons, including so-called 'mini-nukes', have been published by a nuclear watchdog in the US.
BBC News Online world affairs correspondent Paul Reynolds considers some of the questions raised.
What are 'mini-nukes'?
The key to understanding mini-nukes is not just their size. As the name implies, they would be very small, perhaps of 1 kiloton - the equivalent of 1000 metric tonnes of explosive. Indeed, their general name is 'small build'.
Their importance would also come from their accuracy. They would be used as 'bunker-busters' or 'earth penetrating weapons', perhaps to incinerate or destroy an underground stockpile of nuclear, biological or chemical weapons, which could not be attacked in any other way.
New guidance systems, based on global positioning satellites, make the use of such weapons possible.
Why has this been raised now?
An independent American nuclear watchdog organisation, the Los Alamos Study Group has got hold of and has published the minutes of a meeting held at the Pentagon on 10 January 2003 at which preparations for a conference on the testing of current nuclear weapons and the design of a new generation of weapons was discussed.
The conference is planned for this August at Stratcom, the Strategic Command headquarters in Nebraska. The weapons listed are: low (radiation) yield, earth penetrating, enhanced radiation (the "neutron" bomb) and 'agent defeating'. Agent defeating refers not to blowing up enemies' agents but to the destruction of chemical and biological agents.
Why do the Americans want such weapons?
They want more flexible weapons and ones that could be used against emerging threats like chemical and biological weapons.
They want weapons that could be used on a battlefield - not against cities but against defined threats which might not be overcome using conventional weapons.
The end of the concept of Mutual Assured Destruction (MAD) which kept a balance of terror with the Soviet Union is of no use against a potential enemy which has smaller weapons of mass destruction or disruption.
Would they be useable?
Some critics say mini-nukes would so powerful that they would spread radiation and, therefore, could not be used without the risk of contaminating large areas.
They might defeat their own object and not be viable battlefield weapons. Other non nuclear options, such as air burst bombs, could, perhaps, be used instead.
However, the fact that the Pentagon is exploring their use indicates that it thinks they could be technically possible.
How long has this been going on?
It grows out of a review of American nuclear strategy in December 2001. The Defence Secretary Donald Rumsfeld introduced a new concept. Instead of the Old Triad in which air-launched and sea-launched missiles and nuclear bombers formed a triangle of nuclear power, a New Triad was put forward. This consists of:
"Offensive strike systems", that is, the whole of the Old Triad.
"Defenses", including the National Missile Defence System or anti ballistic missile defence.
"A revitalized defense infrastructure that will provide new capabilities in a timely fashion to meet emerging threats."
This means mini-nukes and their kind and the ability to design and produce them in a five year time frame.
Wouldn't this encourage nuclear proliferation?
Anti nuclear groups fear that where the United States treads, others will eventually follow. The Los Alamos Group says the plans call into question the American commitment to article 6 of the Nuclear Non-Proliferation Treaty. This says that "Each of the Parties to the Treaty undertakes to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament┐"
The Treaty is essentially a bargain under which states without the bomb agree not to develop it if states with it move towards nuclear disarmament. This has not worked out in practice.
What happens now?
The Americans are quite well advanced in their planning, according to the leaked documents. There is, therefore, every reason to think that in due course they will develop some, at least, of the weapons they are examining.
Other countries will take a close interest and some might try to build their own. A new concept of warfare is being developed.
What else is being discussed?
One of the problems the US (and other nuclear countries) faces is keeping its nuclear arsenal "up-to-date". It has had a moratorium on live nuclear testing since 1992 yet testing is the best way of checking that device has not deteriorated.
The leaked minutes show that it is very worried about this problem and the question is raised as to whether there could be 'low yield' testing.
That would raise the issue of nuclear testing again.