Afghan security forces and British soldiers inspect the site of a suicide attack in the heart of Kabul, Afghanistan, on Saturday. Three American civilian contractors are reportedly among the dead. Massoud Hossaini/AP hide caption

itoggle caption Massoud Hossaini/AP

Afghan security forces inspect a suicide bombing attack on Aug. 10 near the main gate of Kabul's international airport. It was one of a series of recent attacks in the Afghan capital that have left at least 50 dead. Violence in Afghanistan has increased since U.S. combat troops pulled out last year. Massoud Hossaini/AP hide caption

itoggle caption Massoud Hossaini/AP

This photo provided by the U.S. Government, presented during a trial, shows a photo of Irek Hamidullin surrendering after being wounded by U.S. forces in Afghanistan on Nov. 29, 2009. AP hide caption

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John Sopko, special inspector general for Afghanistan reconstruction, testifies on Capitol Hill last June. In a letter released Thursday, Sopko says the U.S. may have been paying for "ghost schools, ghost students and ghost teachers" in Afghanistan. Charles Dharapak/AP hide caption

itoggle caption Charles Dharapak/AP