Defense Secretary Leon E. Panetta walks to his vehicle after being greeted by Ryan Crocker (right), U.S. ambassador to Afghanistan, and Gen. John Allen (left) upon arriving in Kabul, Afghanistan, on Tuesday, Dec. 13, 2011. (AP Photo/Pablo Martinez Monsivais, Pool)

Photo by: Pablo Martinez Monsivais

Defense Secretary Leon E. Panetta walks to his vehicle after being greeted by Ryan Crocker (right), U.S. ambassador to Afghanistan, and Gen. John Allen (left) upon arriving in Kabul, Afghanistan, on Tuesday, Dec. 13, 2011. (AP Photo/Pablo Martinez Monsivais, Pool)