U.S. soldiers with the NATO led International Security Assistance Force (ISAF) stand guard at the scene of a suicide attack in Kandahar south of Kabul, Afghanistan, Thursday, Jan. 19, 2012. In a separate incident, a senior U.S. defense official says all six reported killed in the crash of a U.S. helicopter in Afghanistan were U.S. Marines. (AP Photo/Allauddin Khan)

Photo by: Allauddin Khan

U.S. soldiers with the NATO led International Security Assistance Force (ISAF) stand guard at the scene of a suicide attack in Kandahar south of Kabul, Afghanistan, Thursday, Jan. 19, 2012. In a separate incident, a senior U.S. defense official says all six reported killed in the crash of a U.S. helicopter in Afghanistan were U.S. Marines. (AP Photo/Allauddin Khan)