US President Barack Obama urged world leaders on Friday to do more to safeguard vulnerable nuclear facilities to prevent "madmen" from groups like DAESH from getting their hands on an atomic weapon or a radioactive "dirty bomb."
He said that the world faced a persistent and evolving threat of nuclear terrorism despite progress in reducing such risks, but he insisted, "We cannot be complacent."
According to Obama no group has so far succeeded in obtaining nuclear materials but Al Qaeda has long sought them and said DAESH's recent attacks in Paris and Brussels have raised similar concerns.
"There is no doubt that if these madmen ever got their hands on a nuclear bomb or nuclear material, they would certainly use it to kill as many innocent people as possible," he said.
"It would change our world."
— The White House (@WhiteHouse) 1 Nisan 2016
Obama hosted more than 50 world leaders for his fourth and final summit focused on efforts to lock down vulnerable atomic materials to prevent nuclear terrorism, which he called "one of the greatest threats to global security" in the 21st century. North Korea's nuclear posturing was also high on the agenda.
A boycott by Russian President Vladimir Putin, unwilling to join in a US-dominated gathering at a time of increased tensions between Washington and Moscow over Ukraine and Syria, added to doubts that the meeting would yield any major results.
Deadly bomb attacks in Brussels last month have fuelled concerns that DAESH could eventually target nuclear plants, steal materials and develop radioactive dirty bombs. Terrorists were found to have videotaped the daily routine of a senior manager of a Belgian nuclear plant, Obama said.
Obama said the required 102 countries had now ratified an amendment to a nuclear security treaty that would tighten protections against nuclear theft and smuggling.
"Our nations have made it harder for terrorists to get their hands on nuclear materials. We have measurably reduced the risks," he said.
But he acknowledged that with roughly 2,000 tonnes of nuclear material stored around the word, not all of this is properly secured.
Focus on Iran, North Korea
The United States and Japan also announced they had completed the long-promised task of removing all highly enriched uranium and separated plutonium fuels from a Japanese research reactor. Japan is strongly against nuclear weapons state due to being the only country to have suffered a nuclear attack.
Despite significant strides by Obama in persuading dozens of countries to rid themselves of bomb-making materials or reduce and safeguard stockpiles, much of the world's plutonium and enriched uranium remains vulnerable to theft.
Earlier on Friday, Obama convened a separate meeting of the world powers that negotiated a landmark nuclear pact with Iran last July, a critical component of his nuclear disarmament agenda and a major piece of his foreign policy legacy.
He said efforts to implement the deal, which required Tehran to curb its nuclear program in return for sanctions relief, had shown "real progress" but it would take time for Iran to reintegrate into the global economy.
Obama inaugurated the first Nuclear Security Summit nearly six years ago, after a landmark speech in Prague in 2009 laying out the goal of a world free of nuclear weapons.
After Obama leaves office there is no guarantee his successor, who will be elected in November, will keep the issue a high priority.
For now, however, US experts are less concerned about terrorists obtaining nuclear weapon components than about thefts of ingredients for a low-tech dirty bomb that would use conventional explosives to disperse radioactive material and sow panic.
US officials said they had no doubt that DAESH, which controls swaths of Syria and Iraq, was interested in obtaining such materials, but authorities had no explicit evidence that the group had tried to do so.
Obama held a special summit session to coordinate the overall fight against DAESH. He touted gains against the group in Iraq and Syria, which he said were forcing it to lash out elsewhere, and called for stepped-up efforts to stem the flow of foreign fighters to and from the battlefield.
He pledged to deploy more US "surge teams" to Europe soon to bolster such operations.
Also looming over the summit was continuing concern about North Korea. Obama joined South Korean President Park Geun hye and Japanese Prime Minister Shinzo Abe on Thursday in vowing to ramp up pressure on Pyongyang in response to its recent nuclear and missile tests.
But So Se Pyong, North Korea's ambassador to the United Nations in Geneva, told Reuters on Friday that Pyongyang will pursue its nuclear and ballistic missile program in defiance of the United States and its allies, saying there is now a state of "semi-war" on the divided peninsula.