Chairman of the US Joint Chiefs of Staff Gen. Martin Dempsey arrived on a surprise visit to Afghanistan Saturday for talks with ISAF leaders and Afghan President Hamid Karzai.The US top military officer plans to huddle with the new overall commander of coalition forces, Gen. Joseph Dunford, and talk with soldiers in the field.Among the key issues for Dempsey is the pacing of US troop withdrawals this year and next, as well as the rate of improvement among Afghan security forces.US President Barack Obama has not announced how many American troops he intends to keep in Afghanistan after 2014, but it will probably be 9,000 to 10,000.