The United States officially ended its eight-and-a-half year military campaign in Iraq Thursday, as the flag of the command was lowered in Baghdad.

Defense Secretary Leon Panetta arrived in Baghdad earlier Thursday morning for the ceremony.

Panetta is scheduled to speak at the event, along with the chairman of the Joint Chiefs of Staff Gen. Martin Dempsey and U.S. Ambassador Jim Jeffrey.

President Jalal Talabani will also be present, among other top Iraqi officials, but it is not clear if Prime Minister Nuri al-Maliki will attend, an American official said.

Panetta will speak about how "Iraq really was pulled back from the brink and that we've been able to maintain those gains even as we've extracted ourselves from the equation over the last three years," the senior defense official told reporters.

Panetta plans to thank the U.S. troops who have served there, as well as Iraqi security forces "for their tremendous sacrifices over the last 8-plus years of the war," said the official, who briefed journalists traveling with Panetta.

The flag of the command was lowered, rolled, and placed in a case during the ceremony. That marked the official end of the mission that began with the United States-led invasion of Iraq in March 2003, aimed at toppling Saddam Hussein.

His regime fell in a matter of weeks, and he was captured in December 2003 after months in hiding, then executed after a trial by Iraq's new authorities.

All U.S. troops must be out of Iraq by the end of this month after Washington and Baghdad failed to agree on terms under which they could remain.

There were about 5,500 American troops in Iraq as of Tuesday, the most recent day American officials in Iraq gave CNN figures.

Obama on Wednesday welcomed home returning troops from Iraq, hailing their service to help a people they didn't know as an example of what makes America great.

"As your commander in chief, and on behalf of a grateful nation, I'm proud to finally say these two words, and I know your families agree -- welcome home. Welcome home," Obama told cheering troops at Fort Bragg, North Carolina.

Obama used his Ft. Bragg speech to mark the fulfillment of a campaign pledge he made in 2008 to end the war.

Noting the nearly 4,500 Americans killed and more than 30,000 injured, Obama spoke of the heavy sacrifice and hard work in the Iraq mission.

"Because of you -- because you sacrificed so much for a people that you had never met, Iraqis have a chance to forge their own destiny," Obama said. "That's part of what makes us special as Americans. Unlike the empires of old, we did so not for territory or for resources. We do it because it's right.

"There can be no fuller expression of America's support for self-determination than our leaving Iraq to its people. That says something about who we are."

Source: CNN