[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/02/11/art.brennan.file.gi.jpg caption ="National Security Advisor John Brennan said Tuesday that troop levels in Iraq will continue to diminish throughout 2011."](CNN) - John Brennan, the president's national security adviser for homeland security, said Tuesday that the total number of U.S. troops in Iraq will continue to diminish throughout 2011, but that noted that the withdrawal rate will be "calibrated and adjusted based on conditions on the ground."
All U.S. combat forces are scheduled to be out of Iraq by December 31, 2011.
The total number of U.S. troops in Iraq has now fallen below 50,000. The U.S. military mission in Iraq will officially switch to an "advise-and-assist" role starting September 1.