U.S. President Barack Obama says the selection of South Korea as the host of the next Nuclear Security Summit reflects South Korea's leadership regionally and globally.

During the inaugural Nuclear Security Summit in Washington Tuesday, Obama also thanked President Lee and the South Korean people for their willingness to accept the responsibility of hosting the nuclear gathering.

Obama said his call last year in Prague for a new international effort to secure all nuclear materials around the world in four years is part of a broader, comprehensive agenda that the United States is pursuing for the ultimate goal of establishing a world without nuclear weapons.

He added that terrorist networks have tried to acquire nuclear weapons, and if they ever succeeded, they would surely use them.