Angela Merkel, Germany's chancellor, speaks to United States President Barack Obama, not pictured, during a bilateral meeting at the Nuclear Security Summit in Washington, D.C., U.S., on Tuesday, April 13, 2010.  Obama urged world leaders today to confront the prospect of nuclear terrorism and take concrete action to head off what he called one of the greatest threats to global security. .Credit: Andrew Harrer / Pool via CNP
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