White House officials say Robert Gates has been sworn in as secretary of defense to replace Donald Rumsfeld.
Gates took the oath of office during a private event at the White House early Monday. A ceremonial swearing-in will take place later Monday, at the Pentagon.
President Bush named Gates to the job last month, saying he wanted a fresh perspective on the situation in Iraq.
Gates has warned Iraq must be stabilized in the next year or two, or the situation may trigger a regional conflict. During his Senate confirmation hearing, Gates said "no" when asked if the United States is winning the war in Iraq.
The 63-year-old is a former director of the Central Intelligence Agency. Before being nominated to the Defense Department post, Gates was a member of the Iraq Study Group panel which earlier this month presented recommendations to the President for redirecting the war in Iraq.
He replaces Donald Rumsfeld, who served as defense secretary under President Bush for six years.
Some information for this report was provided by AP and Reuters.