US President Barack Obama declared the world safer after a 47-nation summit agreed to a four-year deadline to lock down loose nuclear materials to prevent them from falling into militant hands.
"Because of the steps we've taken the American people will be safer and the world will be more secure," Obama said at the end of the summit Tuesday in Washington.
The unprecedented gathering met a challenge laid down by Obama, who said the world was littered with poorly guarded fissile material and that a nuclear-armed militant group could threaten global "catastrophe."
"We welcome and join President Obama's call to secure all vulnerable nuclear material in four years, as we work together to enhance nuclear security," the leaders said in a joint statement.
Hosting the largest summit in the United States in over six decades, Obama also pressed China and other UN Security Council skeptics to back UN sanctions on Iran over its controversial nuclear program.
"I am going to push as hard as I can to make sure that we get strong sanctions that have consequences for Iran," Obama said.
Amid mixed signals from Beijing, Chinese President Hu Jintao told the summit that China "firmly" opposes atomic weapons proliferation, while backing civilian uses.
Beijing kept the world guessing, though, as to whether it would fully endorse the US-led push for a fourth set of UN sanctions on Iran, although a Chinese official said later Tuesday it was ready to discuss "new ideas."
In a boost to Obama however, several countries including Ukraine, Mexico and Canada declared their intention to give up highly-enriched uranium at the summit. And Russia and the United States signed a protocol to get rid of 34 tons of plutonium each, equivalent to 17,000 weapons.
Russian President Dmitry Medvedev hailed the summit as a "full success" as Moscow announced plans to shut down its last weapons-grade plutonium reactor.
A Russian official, who spoke on condition of anonymity, provided no further details but confirmed to AFP that Medvedev had unveiled the plans at the summit.
Obama welcomed the move, calling the closure of the Soviet-era site in Siberia an "important step" for bolstering nuclear security.
On what are commonly referred to as loose nukes, Obama pressed his guests "not simply to talk, but to act."
Nuclear material "that could be sold or stolen and fashioned into a nuclear weapon exist in dozens of nations," he said.
He added that Al-Qaeda had tried to obtain a nuclear bomb, and that radioactive material as small as an apple was enough to kill thousands of people.
"It would be a catastrophe for the world - causing extraordinary loss of life, and striking a major blow at global peace and stability."
The summit leaders agreed in their communique to non-binding, only partly defined measures to combat nuclear trafficking, including sharing information and detection, forensics and law enforcement expertise.
They said they "recognize the need for cooperation among states to effectively prevent and respond to incidents of illicit nuclear trafficking."
But increased security must "not infringe upon the rights of states to develop and utilize nuclear energy for peaceful purposes and technology," summit participants said.
They also reaffirmed "the essential role" of the International Atomic Energy Agency - the UN nuclear watchdog -- and vowed to support the agency.
In a statement from the group's headquarters in Vienna, IAEA chief Yukiya Amano thanked the world leaders "for the moral and political support" they gave his agency.
Amano, who attended the summit, said he was "pleased" that the IAEA's activities "are recognized at the highest levels of government."
Experts said afterwards that Obama's goals, while lofty, were by no means assured.
"I think it's ambitious, it's underfunded and it's going to take a lot effort by the United States and other countries to make it work," Ken Luango, president for Partnership for Global Security, told AFP.
Meanwhile, Obama appealed for 10 billion dollars in an initiative with Canada to improve nuclear security worldwide.
The US leader also addressed fears about the nuclear arsenal in Pakistan, a major stronghold for Al-Qaeda and militant groups at war with US forces in Afghanistan, saying he felt "confident" about security levels.
"But that doesn't mean that there isn't improvement to make," Obama said.
A manual on securing stocks of separated plutonium and weapons grade uranium, as well as advice on how to dispose of the dangerous materials, was issued at the end of the summit.
However, all the steps are voluntary and the timetable for accomplishing the four-year plan remains sketchy.
The next nuclear security summit meeting will be held in South Korea in 2012, where press on Wednesday said the occasion should be used to persuade North Korea to disarm.