NEW : Cameron says a WikiLeaks reference to a lack of troops in the past is trueAfghan president WikiLeaks expresses his gratitude for Afghanistan 's support . U.S. Marines troops could start heading home by the end of 2011 . Cameron 's goal is to turn over security operations in Afghanistan before the end of 2011 .
NEW : Cameron says a WikiLeaks reference to a lack of troops in the past is trueAfghan president Hamid Karzai expresses his gratitude for Britain 's support . British troops could start heading home by the end of 2011 . NATO 's goal is to turn over security operations in Afghanistan before 2015 .