WASHINGTON (CNN) -- The Pentagon shook up the ranks of U.S. commanders in Iraq on Friday, bringing home the top American general there and replacing him with a general who has served there twice before.

Gen. George Casey, the commander of U.S. and allied troops in Iraq, will return to Washington to serve as chief of staff of the Army, Defense Secretary Robert Gates announced Friday afternoon. Lt. Gen. David Petraeus, the former head of the Army's 101st Airborne Division, will be promoted to four-star rank and replace Casey at the U.S. command in Baghdad.

Meanwhile, Adm. William Fallon, now head of the U.S. Pacific Command, will replace the retiring Gen. John Abizaid as the chief of Central Command -- the headquarters of American forces in the Middle East and Central Asia, overseeing the wars in Iraq and Afghanistan.

High-ranking military sources had told CNN the moves were coming earlier Friday. All the appointments will require Senate confirmation.