The US flag is to be lowered in Baghdad, formally marking the end of US military operations in Iraq after nearly nine years of war.

驻巴格达美军将降下国旗，宣告美军在伊拉克9年军事行动的正式结束。

Most of the 5,500 remaining soldiers have now left Iraq, with security in the hands of the Iraqi authorities.

President Barack Obama, who came to office pledging to bring troops home, said the US left behind a "sovereign, stable and self-reliant Iraq".

Some 4,500 US soldiers and more than 100,000 Iraqis have died in the war.

It has cost the US some $1tr.

Republicans have criticised the pullout citing concerns over Iraq's stability, but most Americans support the move.

In a speech to troops just returned from Iraq in North Carolina on Wednesday, Mr Obama hailed the "extraordinary achievement" of the military and said they were leaving with "heads held high".

"Everything that American troops have done in Iraq, all the fighting and dying, bleeding and building, training and partnering, has led us to this moment of success," he said.

"The war in Iraq will soon belong to history, and your service belongs to the ages."

He said the war had been "a source of great controversy¹" but that they had helped to build "a sovereign, stable and self-reliant Iraq, with a representative government that was elected by its people".

Some 1.5 million Americans have served in Iraq since the US invasion in 2003. In addition to those who died, nearly 30,000 have been wounded.

Troop numbers peaked at around 170,000 during the height of the so-called surge strategy in 2007, but as of this week only about 5,500 remained. Many of them have already left for bases in Kuwait prior to flying home.

The last combat troops left Iraq in August last year. A small contingent²（分遣队） of some 200 soldiers will remain in Iraq as advisers³, while some 15,000 US personnel are now based at the US embassy in Baghdad - by far the world's largest.