Unswayed by anti-war passions, President George W Bush said he will send 21,500 additional US Forces to Iraq to break the cycle of violence and "hasten the day our troops begin coming home." He acknowledged making mistakes in earlier security efforts in Baghdad.
The troop buildup will push the American presence in Iraq toward its highest level and put Bush on a collision course with the new Democratic Congress. It also runs counter to advice from some generals.
Bush was to announce the buildup in an evening speech to the United States on Wednesday. Excerpts of his remarks were released in advance by the White House.
The president said Iraq must meet its responsibilities, too - but he put no deadlines on Baghdad to do so.
"America's commitment is not open-ended," he said. "If the Iraqi government does not follow through on its promises, it will lose the support of the American people and it will lose the support of the Iraqi people."
Bush readily acknowledged making mistakes in previous efforts to quell the near-anarchy in Baghdad. "There were not enough Iraqi and American troops to secure neighbourhoods that had been cleared of terrorists and insurgents," the president said. "And there were too many restrictions on the troops we did have."
He said Iraqi Prime Minister Nouri al-Maliki had promised that US Forces would have a free hand and that "political or sectarian interference will not be tolerated.