The White House on Friday warned that al-Qaida is quietly hunting for an atomic bomb, adding urgency to a historic summit next week where President Barack Obama will try to persuade world leaders to step up efforts to keep nuclear weapons out of terrorist hands.
Expectations for decisive action by the 47 countries are low, because existing controls haven't worked as well as hoped and some nations worry tighter regulation will only slow civilian nuclear power projects.
But the White House has high hopes for the two-day summit, where the U.S. and Russia are to sign a long-delayed agreement to dispose of tons of weapons-grade plutonium from Cold War-era nuclear weapons. That is the kind of preventive action the summit is meant to inspire.
Secretary of State Hillary Rodham Clinton said the gathering will be the largest assembly of world leaders hosted by an American president since the 1945 San Francisco conference that founded the United Nations.
Clinton said some attendees are "helping us keep a very close watch on anyone we think could be part of a network that could lead to the sale of or transfer of nuclear material to al-Qaida or other terrorist organizations."
Meeting leaders of India, Pakistan
Obama will try to set the tone Sunday by meeting the leaders of India and Pakistan — two nuclear-armed foes who have managed to avoid atomic war — as well as South Africa and Kazakhstan, two countries that voluntarily gave up nuclear weapons programs.
The conference itself will open Monday with a working dinner hosted by Obama, who also plans to meet individually that day with the leaders of Jordan, Malaysia, Armenia and China. It will close Tuesday with a joint statement on the threat of the illicit transfer of nuclear materials and technology and a plan for keeping them locked up.
Three countries at the heart of the international debate over nuclear dangers — Iran, North Korea and Syria — were not invited to the summit, and Israel, whose undeclared nuclear arsenal is a core grievance among Muslim nations, scrapped plans for Prime Minister Benjamin Netanyahu to attend.
An Israeli official said Netanyahu canceled after getting word that other participants would use the summit to criticize Israel's nuclear program. Israel is believed to have dozens, perhaps hundreds, of nuclear weapons. In Netanyahu's absence, Israel will be represented by Deputy Prime Minister Dan Meridor.
Clinton welcomed Israel's participation.
"Israel shares with us a deep concern about Iran's nuclear ambitions and also about the threat of nuclear terrorism," she said.
Ignoring Israel's arsenal?
Iran and other Muslim countries accuse the United States of hypocrisy for ignoring Israel's nuclear arsenal while demanding that others forego such weapons.
In the U.S. view, a nuclear-armed Iran would threaten Israel and the West, while North Korea, which has tested a nuclear device, is a continuing threat to sell its nuclear know-how to other hostile nations.
The U.S. believes Syria also has nuclear ambitions; an Israeli airstrike in 2007 destroyed what the U.S. asserts was a nearly completed nuclear reactor designed to make plutonium.
But the nuclear security summit is less concerned with countries that acquire nuclear weapons than with the terrorists and criminals believed to be seeking them.
Obama has set a goal of securing all of the world's nuclear materials from theft or diversion within four years, and he hopes next week's summit will endorse that objective.
Gary Samore, Obama's chief adviser on limiting the spread of nuclear weapons, said a number of countries are expected to announce Monday that they are taking unilateral actions.
That may include plans to retrofit nuclear reactors to use a form of uranium fuel less easily converted to use in weapons. Some countries are expected to announce their intent to sign international conventions on nuclear security.
Reactors seen as vulnerable
The 1980 Convention on the Physical Protection of Nuclear Material, for example, was amended in 2005 to require states to protect such materials even when not in transit. The convention also expands measures to prevent nuclear smuggling.
But not enough countries have approved the 2005 amendment to put it into force, and the White House hopes to persuade countries attending the summit to accept it.
Sharon Squassoni, a nuclear expert at the Center for Strategic and International Studies, estimates there are 500 tons of weapons-usable materials in civilian and military reactors that could be targets for sabotage or diversion.
The summit's main focus, Samore said, will be on keeping two key ingredients for a nuclear bomb — plutonium and highly enriched uranium — from traffickers and terrorists.
Thomas Cochran, senior staff scientist at the Natural Resources Defense Council, said Friday that the top security priority should be highly enriched uranium, which is easier than plutonium to engineer into a weapon.
"A crude but potentially devastating nuclear device can be made with as much of this material as would fit in a six-pack of soda cans," Cochran said.
Fear of nuclear terror crystallized after the Sept. 11, 2001, attacks on New York and Washington. Obama last week declared that it poses a graver danger than the risk of war between nuclear nations.
Not all countries share the Obama administration's view of the threat; some worry more about countries like Iran, North Korea and Syria illicitly developing a nuclear arsenal.
Ben Rhodes, a deputy national security adviser, said Friday that the threat of nuclear-armed terrorists is urgent.
"We know that terrorist groups, including al-Qaida, are pursuing the materials to build a nuclear weapon and we know that they have the intent to use one," Rhodes said.
Clinton described the threat in stark terms Friday in a speech in Louisville, Ky.
"A 10-kiloton nuclear bomb detonated in Times Square in New York City would kill a million people," Clinton said, referring to a weapon with explosive power about half that of the U.S. bomb dropped on the Japanese city of Nagasaki in August 1945, killing an estimated 80,000.
"Many more would suffer from the hemorrhaging and weakness that comes from radiation sickness," she added. "Beyond the human cost a nuclear terrorist attack would also touch off a tsunami of social and economic consequences across our country."
Although Iran will not attend the summit, its nuclear program is likely to come up there. Obama is pushing for a U.N. Security Council resolution calling for additional sanctions against Iran.