World leaders head to US nuclear summit

World leaders have begun arriving in Washington for a two-day summit aimed at securing the world's loose nuclear material. U.S. President Barack Obama has invited 46 heads of state and government representatives to the Nuclear Security Summit which officially starts on Monday, Obama has voiced his optimism that countries attending the summit would "make enormous progress" on both the commitment and specific steps to secure nuclear weapons and nuclear material. He called the prospect of nuclear terrorism the single biggest threat to U.S. security.

Barack Obama said, "And we know that organizations like al Qaeda are in the process of trying to secure nuclear weapons or other weapons of mass destruction and would have no compunction at using them. Unfortunately, we have a situation in which there is a lot of loose nuclear material around the world, and so the central focused goal of this summit is getting the international community on a path in which we are locking down that nuclear material in a very specific timeframe with a specific work-plan.

President Obama and Secretary of State Hillary Rodham  Clinton head over from the White House to Blair House  for meetings. (Olivier Douliery / Pool Photo / April 11, 2010)