(Bloomberg) -- Iraqi leaders must "match the courage" of their citizens and form a government to rule their war-shattered country, U.S. Vice President Joe Biden said as American troops formally ended their Iraq combat mission today. Iraqis showed in elections earlier this year that "they expect a government that reflects the results of the votes they cast," Biden said at a ceremony to hand control of the U.S. mission to a new commander, Lieutenant General Lloyd Austin. "That's going to require Iraqi politicians to place the national interest above their own." The ceremony marking the reduction to 50,000 U.S. forces after more than seven years of combat came the day after President Barack Obama used an Oval Office address to declare the combat mission over and cast economic revival as his "central mission." The State Department will take over the lead U.S. role in Iraq.

The success of the U.S. troop surge in 2007 has "given Iraq a shot at a future that it clearly didn't have in 2006 and 2007," Admiral Mike Mullen, the chairman of the U.S. Joint Chiefs of Staff, told reporters before the ceremony.

More than 1 million American soldiers have served in Iraq, Biden said. In addition to the more than 4,400 Americans who lost their lives, Biden said "tens of thousands" of Iraqi security forces and innocent civilians have been killed.

Deadlock Over Government

Iraq's leaders have failed to form a new government almost six months after parliamentary elections. Biden is seeking to cajole Iraqi politicians to break the deadlock.

"I strongly urge them to match the courage that their citizens have shown by bringing this process to a close and forming a government," Biden said.

As insurgents test the Iraqi security forces and their U.S. partners with high-profile attacks, Biden said the American brigades left behind to advise and assist the Iraqi forces are "as combat-ready as any in our military."

A new government is the crucial next step toward stabilizing Iraq, Mullen said. "I worry that, in time, without that government standing up, that certainly opens the door for tensions to rise," he said. The handover ceremony took place below a chandelier in a central rotunda of Saddam Hussein's former al-Faw palace, which became the headquarters for U.S. forces at Victory Base outside Baghdad. U.S. soldiers watched from marble balconies on two floors around the hall draped with American and Iraqi flags, and a military band played both countries' national anthems.

Avoiding 'Strategic Disaster'

Defense Secretary Robert Gates credited General Ray Odierno, the outgoing U.S. commander in Iraq, and his troops for helping avert what could have become a "strategic disaster for the United States."

Odierno said Iraqi security forces are prepared to defend their country, and the U.S. forces that remain "must maintain strategic patience."

Iraq's Prime Minister Nuri Al-Maliki pledged that Iraq won't return to sectarian conflict as U.S. troops pull out, and said Iraq's army is "fully capable and able to carry the responsibility." He also urged all Iraqi parties to join in a "government of national partnership." Flying toward Baghdad earlier today, Mullen said he was "stunned" by the absence of U.S. military hardware in the countryside around the capital, as a result of the withdrawal. "There was so much stuff that wasn't there that had been there for every trip that I've been on since 2004," he said. The equipment was an illustration of the troop surge. "One of the things that I think we have a tendency to forget is how desperate we were in that fight" before the change in strategy, Mullen said. "When you consider how rapidly we shifted, there are some hard lessons in that." The military can't take on such a mission alone and needs the State Department and U.S. foreign aid to play their roles in governance and development, Mullen said. The military also needs to be better prepared with an emphasis on training in the culture of the area and its language, Mullen said. The U.S. must work more often with partner countries, as in the coalition of more than 40 nations fighting in Afghanistan, he said.

By Viola Gienger

With assistance from Peter S. Green in New York, Roger Runningen, Nicholas Johnston and Julianna Goldman in Washington. Editors: Robin Meszoly, Laurie Asseo.