President Obama has spoken of his hopes for a nuclear-weapons free world.
On 24 September 2009, the UN Security Council, adopted a resolution (1887) calling for the creation of "conditions for a world without nuclear weapons... "
Is a nuclear-weapons free world possible?
It is possible but unlikely for the foreseeable future. Even President Obama said that he did not expect to see it in his lifetime and also said that as long as such weapons existed, the US would keep its own nuclear arsenal.
In the meantime, he is reported to be wanting far fewer US nuclear warheads (in the hundreds rather than thousands) and he wants the US Senate to ratify the comprehensive test ban treaty. On 4 May 2010, the US disclosed that it has 5113 warheads in its nuclear stockpile.
There is no suggestion that nuclear-weapon states are ready to disarm completely.
Russia and China have both announced upgrades to their nuclear arsenals and so has the UK, with a plan to build four new submarines with Trident missiles.
However British Prime Minister Gordon Brown has proposed that, as part of an overall agreed package, Britain might build three submarines not four.
Are not the nuclear states supposed to be disarming under the NPT?
Yes but by how much is a subject for debate. The main issue is the interpretation of the Nuclear Non-Proliferation Treaty Article VI. The treaty was basically a bargain agreed in 1968 between nuclear-armed and non-nuclear-armed states.
The nuclear-weapon states - the US, Russia (then the Soviet Union), China, Britain and France - were allowed to keep their weapons but not to give them to anyone else. The non-nuclear-weapon states were allowed to develop nuclear technology but only for peaceful purposes.
The treaty also laid disarmament obligations on the nuclear states. These states say they are in compliance with the treaty, but critics say the treaty requires further, indeed complete, nuclear disarmament.
What exactly does the NPT say?
The key passage on the issue, Article VI, says: "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, and on a Treaty on general and complete disarmament under strict and effective international control."
What does it mean?
Interpretations of it vary, and this is the problem.
What do critics of the nuclear-weapon states argue?
They say the article clearly implies that nuclear-weapon states should start with an early end to the arms race, move onto negotiations leading to nuclear disarmament and then, with all other states, agree on a treaty on general disarmament.
These campaigners quote an advisory opinion from the International Court of Justice in 1996 that "there exists an obligation to pursue in good faith and bring to a conclusion negotiations leading to nuclear disarmament in all its aspects under strict and effective international control."
They also quote a final statement from the 2000 NPT Review Conference in which one of the steps agreed was "an unequivocal undertaking by the nuclear-weapon States to accomplish the total elimination of their nuclear arsenals leading to nuclear disarmament to which all States parties are committed under Article VI."
What do nuclear-weapon states say?
They say they are committed by treaty only to "negotiations in good faith on effective measures" relating to the nuclear arms race and to nuclear disarmament and that they have fulfilled this by reducing their nuclear arsenals.
They are not committed in the treaty, they say, to total nuclear disarmament. They also argue that there is no time-frame, other than to end the arms race "at an early date".
They also argue that the ICJ ruling was not binding. As for the 2000 NPT review conference statement, the "unequivocal undertaking" demanded of them was contingent on wider disarmament and the subsequent 2005 review conference reached no such conclusion.
Is the NPT legally binding?
The treaty is binding on all states that are parties to it. The problem is that not all member states agree on what the disarmament obligations mean. And states not signed up are under no obligations.
What weapons have the nuclear states given up?
The United States and Russia have substantially reduced their nuclear weapons from the tens of thousands they held during the Cold War. After a series of strategic arms treaties, they agreed the Moscow Treaty in 2002 under which they will both cut their strategic nuclear arsenals to 1,700-2,200 operationally deployed warheads by 2012.
The UK has withdrawn nuclear bombs carried by aircraft and has cut the warheads deployed on its four submarines to 48 at any one time and to fewer than 200 in total. France withdrew its nuclear bombers and cut its submarines from five to four.
China appears to be the exception. The Pentagon said in 2006 that China was "quantitatively and qualitatively" improving its long-range nuclear missile force.
Do the nuclear-weapon states have any intention of giving up nuclear weapons?
Not as things stand.
Are nuclear-weapon states building new nuclear weapons and delivery systems?
Yes. The UK government has decided to replace its Trident submarines, though is offering to build three not four. President Putin said in March 2006 that "Russia must be sure that its nuclear arsenal is up to the demands of the modern world".
The United States and France also intend to keep their weapons up to date and China is believed to be developing new missiles and warheads.
The Pentagon did propose a programme to develop new versions of existing smaller nuclear weapons - one of which is designed as a "bunker buster" - but Congress withdrew funding in 2005.
What about other nuclear-armed states?
India and Pakistan both have nuclear weapons but they are not parties to the NPT and therefore are not restricted. Israel, which is also not in the NPT, is reckoned to be nuclear-armed but it has not confirmed or denied this. North Korea has carried out a nuclear test but has withdrawn from the NPT, as any party to it can.
What pressure is being put on these states?
The Security Council has imposed restrictions on trade in arms and luxury goods with North Korea. Even though North Korea has left the NPT, and therefore in theory has the right to do what it wants, the Council has a right to act because it regards North Korea as a threat to international security.
No UN sanctions have been imposed on India and Pakistan following their 1998 nuclear tests partly because they are not in the NPT and are therefore under no obligations. But they also have had and have powerful friends in Russia and the United States who would have vetoed Security Council sanctions.
The US is supportive of Pakistan, whose help it needs in its war on terror. Even when the Pakistani scientist A Q Khan was found in 2004 to have secretly provided nuclear weapons technology to Iran, Libya and North Korea, Pakistan was not punished by the US.
During the Cold War, the Soviet Union was an ally of India but more recently the US has come closer to India, seeing it as a stable, democratic and increasingly important regional power.
It has signalled its acceptance that India is now a nuclear-armed state. The two countries reached an agreement under which the US lifted a ban on trade in civilian nuclear technology and India agreed to accept IAEA inspection of its civilian nuclear sites.
What about Israel?
Israel is believed to have several hundred warheads and refuses to allow IAEA inspection of its nuclear facilities. In September 2009, the IAEA passed a resolution that "expresses concern about the Israeli nuclear capabilities, and calls upon Israel to accede to the NPT and place all its nuclear facilities under comprehensive IAEA safeguards..."
Israel is criticised for maintaining nuclear weapons and for not agreeing to a nuclear-free Middle East zone. While formally not confirming or denying that they have nuclear weapons, Israeli leaders argue that they need a deterrent. Israel is supported by the United States, which would stop any moves in the UN to impose sanctions.
In May 2010, signatories of the NPT agreed to hold a conference in 2012 to begin the process of establishing a nuclear-weapons-free zone in the Middle East. Arab nations see the regional conference as a first step to disarming Israel's undeclared atomic arsenal.
Are double standards operating against some countries?
It is sometimes argued that certain countries - Pakistan, India and Israel- have been allowed to develop nuclear weapons without too much outside pressure because they are friends of the United States . But others - North Korea, Iran and Libya - are declared threats to international security and face heavy pressure or UN sanctions. In the case of Iran, it has not developed nuclear weapons and says it will not do so but it is developing enrichment technology which can be used both to make nuclear power and a nuclear bomb.
The US response is that there is a difference between the threats posed by some countries and not others. North Korea is seen as an unpredictable and potentially dangerous dictatorship and Iran as a country that cannot be trusted because it hid a uranium enrichment programme for 18 years despite its commitment not to do so under the Nuclear Non-Proliferation Treaty.
Libya is put forward as an example of a country which admitted to a secret nuclear programme and was rewarded with the lifting of trade restrictions.
What about the UK's Trident?
The British government has decided to replace its Trident missile-carrying submarines, though perhaps with three not four vessels. It argues that this would not break its obligations under the NPT, but critics say that a replacement would break what they say is an NPT commitment to nuclear disarmament.
Critics also argue that an agreement between the US and UK on the transfer of nuclear technology - called the Mutual Defence Agreement 1958 - also breaks the NPT. This is because, they say, the NPT forbids the transfer of nuclear weapons, even between nuclear-weapon states. It is also claimed that the renewal of the MDA until 2014 contravenes the NPT's requirement for nuclear disarmament. The UK says that only technology is transferred, so the NPT is not being broken.