WASHINGTON - General David Petraeus, head of U.S. Central Command, has said he is focused on how to get troops into Afghanistan, not how to get them out. August 2011, the target set by U.S. President Barack Obama for the start of U.S. troop withdrawals from Afghanistan, is "some time away in military terms," Petraeus said Thursday at the Center for Strategic and International Studies in Washington. "Right now the emphasis is on the rapid deployment of the new troops," Petraeus said. The president approved an additional 30,000 troops for Afghanistan last December. Petraeus expected that they would all be "on the ground by the end of August." He stressed that August 2011 would mark the "beginning of a transition" to a greater role for Afghan troops but that the pace of U.S. withdrawal would be "conditions-based." "I thought from the start that Afghanistan would be the longest campaign in the 'long war' (against terrorism)," Petraeus said. The United States plans to expand Afghan security forces by 100,000 in the next two years. Petraeus conceded that it was an ambitious target. He said he will divert at least one combat battalion deployed to Afghanistan to the mission of training Afghan troops.