President Barack Obama approved the additional troops for protection of American personnel following a request by the State Department and a review and recommendation by the Defense Department, the White House said in a statement.
The buildup of U.S. troops in Baghdad follows the growing threat from Islamic State militants in northern Iraq. Since early August the U.S. has carried out 124 airstrikes against the militants, the latest taking place near Mosul Dam on Monday.
The additional troops will not serve in a combat role, the White House said. Most are from the Army and some are Marines, the Pentagon said in a statement.
Approximately 820 troops have now been assigned to augment diplomatic security in Iraq, said Rear Adm. John Kirby, the Pentagon's spokesman.
The additional troops will come from within the U.S. Central Command area of operations and will include a headquarters element, medical personnel, associated helicopters and an air liaison team, Kirby said. Fifty-five troops in Baghdad since June will be redeployed outside of Iraq and replaced by 405 newly deployed troops, he said.
The airstrike Monday near Mosul Dam involved fighters and attack aircraft that damaged or destroyed 16 armed vehicles, Central Command said in a statement late Tuesday.