World leaders say nuclear terrorism remains a 'grave threat'

World leaders said Nuclear weapons remain a challenge for the world, during a nuclear summit held in Seoul.

South Korean President Lee Myung-bak said nuclear terrorism remained a "grave threat", while US President Barack Obama said action was key.

The Chinese President, Hu Jintao, urged the group to work together on the issue.

The meeting has so far been dominated by North Korea's plan to launch a rocket next month.

North Korea says the long-range rocket will carry a satellite. However, the US insist that any launch would violate UN resolutions and constitute a missile test.

During the summit, Obama said that the threat of nuclear weapons remains a potent challenge for the globe to confront, telling foreign leaders that "the security of the world depends on the actions that we take."

He said that the international community had made progress in removing nuclear materials and improving security at nuclear facilities around the globe.

As a result, Obama said, more of the world's nuclear materials will not fall into the hands of terrorists.

But he added "there are still too many bad actors in search of these dangerous materials and these dangerous materials are still vulnerable in too many places."