WASHINGTON - Chile has handed over its store of highly enriched uranium to the US in a top-secret mission to spirit the material out of the country - and out of the reach of terrorists.

Details of the operation, which was threatened by February's huge earthquake in Chile, have just emerged but the handover is being hailed as a key example of small country co-operation in the hunt for the world's ''loose nukes''.

The US President, Barack Obama, is expected to make a strong pitch today to the leaders of more than 40 nations who have gathered in Washington to accelerate efforts to secure materials that could be used in a terrorist attack.

The Nuclear Security Summit is expected to approve measures to either repatriate or better secure stockpiles of nuclear material in the 50 or so nations that have nuclear weapons, civilian research reactors, laboratories or power plants.

Mr Obama greeted a number of leaders on Sunday, declaring nuclear terrorism a greater global threat than the Cold War years of nuclear brinkmanship.

Speaking before talks with the South African President, Jacob Zuma, Mr Obama said terrorists were working hard to get their hands on the materials.

''If there was ever a detonation in New York City or London or Johannesburg, the ramifications economically, politically and from a security perspective would be devastating,'' Mr Obama said. ''And we know that organisations like al-Qaeda are in the process of trying to secure a nuclear weapon, a weapon of mass destruction that they have no compunction at using.''

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