US President Barack Obama urged world leaders on Friday to step up efforts to prevent "madmen" from groups such as the Islamic State of Iraq and the Levant (ISIL) from obtaining nuclear weapons, as he announced that 102 nations have ratified a treaty on the protection of nuclear materials.
Speaking at a nuclear security summit in Washington DC, Obama said there was a persistent and evolving threat of nuclear attacks despite progress in reducing such risks.
"We cannot be complacent," Obama said, adding that no group had succeeded in getting their hands on nuclear weapons.
He pointed out, however, that al-Qaeda had long sought them and ISIL (also known as ISIS) had already used chemical weapons, including mustard gas, in Syria and Iraq.
"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," Obama added. "It would change our world."
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The US president was hosting more than 50 world leaders for his fourth and final summit on nuclear security focused on efforts to lock down vulnerable atomic materials to prevent nuclear attacks.
During the summit, Obama announced that the Convention on the Physical Protection of Nuclear Material would take effect soon. The agreement had been in existence for decades. But it was only in the past few weeks that it got the approval of at least two-thirds of all signatory countries, the number required for it to take effect.
The deal requires countries to implement more stringent methods to protect nuclear materials.
"As a result, we expect that the treaty will enter into force in the coming weeks, giving us more tools that we need to work together in the event of theft of nuclear material or an attack on a nuclear facility," Obama said.
North Korea's nuclear defiance was also high on the agenda.
Obama, who is pushing for a significant reduction of nuclear weapon stockpiles, has less than 10 months left in office to follow through on one of his signature policy initiatives.
But there were concerns that Russia's absence from the talks would hinder any real progress. Moscow is refusing to take part because of increased tensions with the US in recent months.
The US and Russia hold more than 90 percent of the world's nuclear arsenal, left over from the Cold War.
The deadly bomb attacks in Brussels last month have increased concerns that ISIL could eventually target nuclear plants, steal material and develop radioactive "dirty bombs".
Obama said suspected members of the armed group were reportedly found to have secretly videotaped the daily routine of a senior manager of a Belgian nuclear plant.
He added that with roughly 2,000 tonnes of nuclear material stored around the word, "not all of this is properly secured".
Al Jazeera's Rosiland Jordan, reporting from Washington DC, said experts have raised concerns that even a small amount of nuclear "raw materials" in the hands of armed groups "would be enough to scare a lot of people".
At the Washington summit, the US 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 project.
Japan is an avowedly anti-nuclear-weapons state as the only country ever to have suffered a nuclear attack.
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 programme in return for sanctions relief, had shown "real progress" but it would take time for Iran to reintegrate into the global economy.
Source: Al Jazeera and agencies