SEOUL -- World leaders gathered for the Seoul Nuclear Security Summit "not to talk but to take actions", US President Barack Obama said during the morning plenary session Tuesday.

The world's governments are fulfilling commitments made in Washington, removing nuclear materials, making more real, tangible steps. More nations come to the table, not to talk but to take actions, said Obama.

"I think we all understand that no one nation can do this alone, and the goal will only be met when we work as an international community. What we did in Washington and what we do in Seoul will be part of a larger global architecture designed to reduce the threat of nuclear terrorism and pursuing peaceful uses of nuclear technology," said Obama.

Leaders and representatives from more than 50 nations and four international institutions are gathering here to discuss the response to combat nuclear terrorism threat, protection of nuclear materials and facilities as well as prevention of illegal trafficking of nuclear materials.