US Vice President Joe Biden, left, Secretary of Defense Robert Gates, 2nd left, attend the United States Forces-Iraq change of command ceremony in Baghdad, Iraq, 01 Sept, 2010.

"We have kept a promise, a promise made to the American people and to the people of Iraq by drawing down our forces to roughly 50,000, and we are on track to remove all of our troops by the end of next year, according to the agreement signed by President Bush, made with the Iraqi government," Biden said.

Biden noted the sacrifice of American and Iraqi forces, and of Iraqi civilians. He noted that more than a million US troops have been assigned to Iraq during the last seven-and-a-half years. And the vice-president said American involvement with Iraq will continue, not only with the thousands of troops advising its military, but with a surge of diplomats and aid workers.

"Our goal is not just a physically secure Iraq, but an economically prosperous and stable one as well," Biden stated.

To that end, the vice president urged Iraqi politicians to end their nearly six-month impasse and form a new government.

Insurgent attacks continue in Iraq, some of them on a very large scale. But Mr. Biden said overall violence in Iraq is at its lowest level since the US-led invasion in 2003.

The outgoing commander, General Ray Odierno, who has spent a total of 55 months commanding troops here at various levels, said this is the right time to end the combat mission. "Even today there are those who doubt that the Iraqi security forces are ready to take full responsibility for security," he said. "I stand before you today and say they are ready to do that task."

Odierno said Iraq will always be a part of him and he looks forward to coming back to visit.

US Defense Secretary Robert Gates, who traveled from Washington for the ceremony, credited General Odierno with successfully implementing the surge and counterinsurgency strategy when it was adopted in 2007, and seeing the job through to the end.

"He helped craft, and implemented the strategy that led to the dramatic decreases in violence of the past three years. Without Ray's and his troops' ability to turn plans into results on the ground, we would be facing a far grimmer situation outside these walls today, and more broadly, a strategic disaster for the United States," Gates said.

The incoming commander, General Lloyd Austin was Odierno's deputy a year ago, and comes directly from the top job on the joint military staff at the Pentagon. "Make no mistake, our military forces here and those of the Iraqi nation remain committed to ensuring that our friends in Iraq succeed, and we will demonstrate our commitment through a continued partnership with the Iraqis," Austin said.

The troops General Austin now commands are fully capable US Army brigades, but their mission is to "advise and assist" the Iraqi Army and police. That means they will sometimes go on patrol with the Iraqis, but their job will be to train and to call in support as needed, not to lead or fight.

Still the substantial number of American troops here can help in an emergency, and analysts say they will also serve as a stabilizing influence to help prevent ethnic and sectarian tensions from again flaring into violence.

atrium: a large high open space in the centre of a modern building （現(xiàn)代建筑物開闊的）中庭，天井

impasse: a difficult situation in which no progress can be made because the people involved cannot agree what to do deadlock（僵局；絕境）

sectarian: connected with the differences that exist between groups of people who have different religious views （宗教）教派的，派性的

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（來源：VOA 編輯：陳丹妮）