World leaders have endorsed US President Barack Obama's call for securing all nuclear materials around the globe within four years to keep them out of the grasp of terrorists. But they offered few specifics for achieving that goal.
The threat of nuclear terrorism was the focus of a 47-nation, two-day summit that ended on Tuesday -- billed as the largest gathering of world leaders on US soil since the UN founding conference 65 years ago.
But it was two nations that were not invited -- Iran and North Korea -- that attracted much of the attention.
Mr Obama had called the conference to focus world attention on the threat of nuclear terrorism, a peril he termed the greatest threat facing all countries and a "cruel irony of history" after mankind had survived the Cold War and decades of fear stoked by a US-Soviet arms race.
The leaders agreed to hold a follow-up nuclear security summit in South Korea in 2012.
A terrorist group in possession of plutonium no bigger than an apple could detonate a device capable of inflicting hundreds of thousands of casualties, he said.
"Terrorist networks such as al-Qaida have tried to acquire the material for a nuclear weapon, and if they ever succeeded, they would surely use it," Obama told the opening session, which convened under tight security at the Washington Convention Center.
Countries said they would cooperate more deeply with the United Nations and its watchdog arm, the International Atomic Energy Agency. They also said they would share information on nuclear detection and ways to prevent nuclear trafficking.
Several countries, including Ukraine, Mexico and Canada, declared their intention to give up highly enriched uranium as a step toward making it harder for terrorist groups or criminal gangs to steal or acquire a key ingredient in the making of atomic weapons. Russia and the US signed a deal to dispose of tons of weapons-grade plutonium, although that won't start for eight years.
In a concluding news conference, Obama said he was confident China would join other nations in pressing for tough new sanctions on Iran for continuing to defy the international community in seeking such weapons.
"Words have to mean something. There have to be consequences," Mr Obama said.