London, Sep 17 : General Ray Odierno, who succeeded General David Petraeus as America's top commander in Iraq, has warned that recent improvements in security were "fragile and reversible."
US Defence Secretary Robert Gates said both generals had formed an "incredible team" during the deployment of 30,000 extra US troops to Iraq last year.
"Progress remains fragile and caution should be the order of the day," Gates said at a formal handover ceremony at a US military base in Iraq.
"Iraq is now a different country from the one I had seen first. However, we must realise that these gains are fragile and reversible," said Odierno.
General Odierno's troops captured Saddam in December 2003 and the general was criticised for using heavy-handed tactics in Tikrit, the former Iraq dictator's hometown. Earlier this year, Gates called him "one of the most effective military leaders of his generation".
General Petraeus has been posted to Tampa, Florida, to command all US forces in the Middle East - from the Horn of Africa to central Asia. He will still deal with Iraq as well as an expanding US military effort in Afghanistan, an al-Qaida revival in neighbouring Pakistan, and the looming confrontation over Iran's nuclear ambitions.
General Petraeus, who is often described as the most influential US general since William Westmoreland of the Vietnam-era, took command of 140,000 US troops in Iraq in early 2007 when suicide bombings and sectarian attacks brought the country to the brink of civil war.