"I am announcing a new international effort to secure all vulnerable nuclear material around the world within four years."

VOA: standard.2010.04.06

But experts say no-one knows how large the world stockpile of nuclear material is because not every country reports what it's producing.

VOA: standard.2010.04.06

Uranium enrichment is the process used to make fuel for nuclear power plants, but when extended it can also produce fissile material for an atomic bomb.

VOA: standard.2009.11.28

The American administration wants agreement from North Korea to inspections by the International Atomic Energy Agency of sites where it is suspected of keeping material for nuclear weapons.

ECONOMIST: Bush's Korean scepticism | The

Before that some of Mr Kim's nuclear material had turned up in Libya, via the nuclear black market, before that country handed in all its bomb-making paraphernalia.

ECONOMIST: North Korea's nuclear spectacular

Iran told the agency that no nuclear material had been introduced into the plant, and enrichment levels would only be high enough to make nuclear fuel, not a bomb.

BBC: Iran 'concealed nuclear facility'