World's security depends on nuke summit: Obama

Nuclear terrorism remains a global threat and the safety of the world depends on decisions taken at a summit in the South Korean capital, US President Barack Obama said Tuesday.

Obama was addressing a 53-nation nuclear security summit dedicated to keeping such material out of the hands of terrorists.

"The security of the world depends on the actions that we take," he told fellow leaders and senior officials at the start of the second and final day.

Obama began the process with a summit in Washington in 2010. The Seoul  gathering will consider progress since then.

"We are fulfilling the commitments we made in Washington," Obama said, adding security at nuclear facilities had been tightened and vulnerable material had been removed or destroyed.

"As a result, more of the world's nuclear material will never fall into the  hands of terrorists who would glady use it against us," he said.

"What's also undeniable is that the threat remains. There are still too many bad actors in search of these dangerous materials and these dangerous materials are still vulnerable in too many places.

"It would not take much -- just a handful of so of these materials -- to kill hundreds of thousands of innocent people."

Obama said that as a consequence of the Seoul summit, "more of our citizens will be safer from the danger of nuclear terrorism".