President Barack Obama rallied world leaders at an unprecedented summit on preventing nuclear terrorism today against a backdrop of a mounting US-led drive to tighten sanctions on Iran.
Hosting a 47-country conference in Washington, Mr Obama called for concerted global action to lock down loose nuclear materials, warning that if al-Qaeda acquired an atomic weapon it would be a "catastrophe for the world."
"Two decades after the end of the Cold War, we face a cruel irony of history - the risk of a nuclear confrontation between nations has gone down, but the risk of a nuclear attack has gone up," Mr Obama said.
"So today is an opportunity not simply to talk, but to act. Not simply to make pledges, but to make real progress for the security of our people," he told the assembled heads of state and government.
US officials sought to focus the summit narrowly on nuclear security and avoid clashes among a fractious group ranging from traditional nuclear powers like Russia and Britain to nuclear-armed foes India and Pakistan.
But on the sidelines of the two-day meeting, Mr Obama has conducted an intensive campaign to ratchet up international pressure on Iran over its nuclear programme.
He secured a crucial pledge from Chinese president Hu Jintao yesterday to help draw up a new UN sanctions package against Iran, US officials said. China gave no specific commitment to back tough punitive measures Washington wants.
Beijing stressed today it wanted any Security Council resolution to promote a diplomatic way out of the nuclear standoff. Iran, which is not attending the conference, is China's third-largest crude oil supplier.
Signalling no let-up in the US push, Secretary of State Hillary Clinton held talks on Iran with representatives of the permanent five Security Council members and Germany last night.
German chancellor Angela Merkel cited "promising signs" of cooperation from China and Russia, both reluctant in the past about imposing further sanctions. "I believe time is pressing," she said in a statement.
Also absent was North Korea, another country regarded by the West as a nuclear threat But Mr Obama sent a clear message to Pyongyang when he announced that South Korea would host the next nuclear security summit in 2012.
Citing nuclear terrorism as the single biggest global security threat, Mr Obama is seeking agreement on an action plan to secure all vulnerable fissile materials worldwide within four years to keep it away from groups like al-Qaeda.
A draft communique being prepared for today's closing session showed the summit was likely to endorse that goal, though the means to accomplish it were expected to be unclear.
Mr Obama's counter-terrorism adviser, John Brennan, said al-Qaeda had made it a top priority to acquire material to make a bomb but had been thwarted so far. He said criminal gangs had scammed al-Qaeda by offering phony materials.
The summit - the biggest hosted by the United States in over six decades - marks a test of Obama's ability to galvanise global action on a broader nuclear agenda that calls for eventually ridding the planet of atomic weapons.
While the summit appeared unlikely to yield any surprise breakthroughs, it has already produced several dividends.
Washington and Moscow planned to sign a deal today to reduce stocks of excess weapons-grade plutonium, with US officials saying each country will dispose of 34 metric tons.
The United States, Canada and Mexico agreed to work together with the International Atomic Energy Agency to convert Mexico's research reactor from the use of highly enriched uranium to low enriched uranium fuel.
Ukraine, which in 1994 gave up nuclear arms inherited in the collapse of the Soviet Union, announced it would get rid of its highly enriched uranium, and Canada said it would return spent nuclear fuel to the United States, its supplier.
Washington is concerned about the security of hundreds of tons of highly enriched uranium and plutonium scattered about the globe in nuclear reactors, research facilities and military installations that may be vulnerable to theft.
After the Cold War, Washington worked with Moscow to improve poor security of nuclear material in Russia and former Soviet republics. Now it wants to broaden these efforts and get countries to crack down on nuclear trafficking.
Reuters