he top U.S. military commander in the Middle East told senators for the first time Tuesday that he had envisioned keeping about 20,000 troops in Afghanistan after combat operations end in 2014, far more than the number the Obama administration and NATO are considering.

Gen. James Mattis, head of U.S. Central Command, said he personally recommended the U.S. leave 13,600 troops in Afghanistan and that he assumed the NATO allies would probably contribute "around 50 percent" of the U.S. total, which would be roughly 6,500."We have to send a message of commitment," Mattis told the Senate Armed Services Committee.U.S. and NATO leaders said last month that they may keep between 8,000 and 12,000 troops in Afghanistan after combat troops leave by Dec. 31, 2014. At a NATO meeting in Brussels, former Defense Secretary Leon Panetta acknowledged the range being considered, but noted that no final decision has been made.

Panetta said that most allied defense ministers assured him they were committed to remaining part of a U.S.-led coalition after combat forces leave Afghanistan.Pressed by senators Tuesday about the possible reduction of troops over time after 2014, Mattis said he would not want to forecast a specific troop withdrawal timetable through 2018 because war is unpredictable."My concern is that at the end here we're going to drop the ball and I don't want to do that," said Sen. Lindsey Graham, a Republican.

Mattis responded that, "if the Afghan security forces continue to mature the way they have been and we hold them at that full strength into 2018, there may be more reductions we can take."U.S. and NATO leaders have said they are strongly considering a plan to continue funding a security force of 352,000 Afghan troops through 2018, as part of an effort to maintain security and help convince Afghanistan that America and its allies will not abandon it once combat troops leave in 2014, senior alliance officials said Thursday.