Day 1 of the Nuclear Security Summit (14 images)

Leaders of about four dozen nations and non-government organizations were called to Washington to discuss security of nuclear materials.

U.S. President Barack Obama convened the high-profile meeting to look into what he called the most severe security issue for the United States -- the possibility that a terror group such as al-Qaida obtained nuclear materials and used them in an attack on U.S. interests.

President Barack Obama and Secretary of state Hillary Clinton walk from the White House to the Blair House to participate in bilateral meetings April 11, 2010 in Washington, DC. UPI/Olivier Douliery/Pool

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President Barack Obama holds a bilateral meeting with Prime Minister Singh of India at the Blair House in Washington, April 11, 2010. UPI/Olivier Douliery/Pool

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President Barack Obama holds bilateral meeting with President Nazarbayev of Kazakhstan at the Blair House April 11, 2010 in Washington, DC. UPI/Olivier Douliery/POOL

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President Barack Obama holds bilateral meeting with President Nazarbayev of Kazakhstan at the Blair House April 11, 2010 in Washington, DC. UPI/Olivier Douliery/POOL

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