Around 50 world leaders have gathered in South Korea to discuss measures to fight the threat of nuclear terrorism, including the protection of nuclear materials and facilities, as well as the prevention of trafficking of nuclear materials.
Barack Obama, the US president, used the opening day of the nuclear security summit to set out a series of wide-ranging goals on nuclear policy. He praised achievements made so far, and promised more would emerge from these discussions.
"We have to question whether the rules we have today are adequate, and my view is that they're totally inadequate. There's no uniformity, no requirement to control materials a certain way."
Kenneth Luongo, Fissile Materials Working Group
The summit represents the half way point of a four-year process set out by Obama with the goal of locking down nuclear materials worldwide and preventing their use in a terrorist attack.
But this year’s summit takes place against a backdrop of growing tensions over the nuclear standoff with Iran and concerns about North Korea's plans to launch a satellite next month - a launch that the US, South Korea and others believe is a missile test.
So, how big a threat is nuclear terrorism? Who sets the criteria for acquiring nuclear weapons? Are there grounds for accusing Western governments of double standards? And can a problem of such magnitude be tackled by voluntary agreements made at the summit?
Inside Story, with presenter Laura Kyle, discusses with Richard Burt, the chief US negotiator in the Strategic Arms Reduction Treaty who is also the US chairman of Global Zero which seeks elimination of nuclear weapons; Mark Hibbs, a senior associate in the Nuclear Policy Program at Carnegie Endowment for International Peace; and Riad Kah-waji with the Institute for Near East and Gulf Military Analysis.
"Even after New Start [Treaty signed with Russia two years ago], the US will still have more than 15,000 deployed nuclear weapons and some 5,000 warheads. I firmly believe that we can ensure the security of the United States and our allies, maintain a strong deterrent against any threat and still pursue further reductions in our nuclear arsenal."
Barack Obama, the US president
Nuclear warheads around the world:
Though the exact number of nuclear weapons in each country's possession is a closely-guarded national secret, there are estimates available.
Of the countries that are members of the non-proliferation treaty:
- Russia is believed to have around 10,000 nuclear warheads
- The US is estimated to have 8,500
- France is believed to have 300
- China is estimated to have 240
- The UK is said to have 225
Of the non-member countries:
- Israel is said to have 80 nuclear warheads, though it refuses to confirm or deny whether it has any
- Pakistan is thought to have between 90 and 110
- India is believed to have between 80 to 100
- North Korea is believed to have enough material to produce up to 10 devices