President Barack Obama grinned and flashed the peace sign as world leaders gathered for a "team photo" during a two-day nuclear summit in Washington, DC.
The summit met to discuss terrorist threats involving nuclear weapons and the recent Iran nuclear deal.
President Obama praised the recent nuclear deal with Iran as a "substantial success" but also spoke of the threat of nuclear weapons falling into the hands of terrorists such as Isis.
Addressing the summit, he said that while no terror group had succeeded in getting hold of enough nuclear materials to make a dirty bomb, al-Qaeda had wanted to and Isis has already used chemical weapons.
He warned that there was no doubt if "madmen" in Isis obtained nuclear material, they would use it to kill as many people as possible.
"We have measurably reduced the risk," he said. But added: "The threat of nuclear terrorism persists and continues to evolve."
During the summit, the president also spoke to the leaders of South Korea and Japan about deterring nuclear provocations from North Korea. He also sat down with Chinese President Xi Jinping to discuss their mutual concern about the North, a traditioanl ally of China.
Undeterred, North Korea fired a short-range missile into the sea hours later.
Russian President Vladimir Putin, whose nuclear weapons stockpile is rivaled only by the stockpile in the US, declined to attend this year's summit.
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