The last convoy of U.S. soldiers has left Iraq, ending an almost nine-year U.S.-led war that ousted Iraqi dictator Saddam Hussein and left a fragile democracy still facing insurgents and sectarian divisions.

The final convoy of 100 U.S. military vehicles carrying about 500 troops crossed into Kuwait Sunday morning , leaving behind several hundred U.S. security personnel at the U.S. embassy in Baghdad. The withdrawal ended a war that cost the lives of almost 4,500 U.S. troops, tens of thousands of Iraqis, and hundreds of billions of dollars of U.S. government funds.

The last U.S. military convoy departed from a base in the southern Iraqi town of Nasiriyah under cover of darkness and secrecy to prevent any final attacks as it drove across a desert highway toward the border. The American soldiers cheered as they entered Kuwait and said they look forward to reuniting with their families.

U.S. Joint Chiefs of Staff Chairman General Martin Dempsey said Sunday the U.S. military will continue its relationship with Iraq through a security cooperation office that will focus on continuing to develop Iraqi security forces.

Speaking to the Al Hurra television network during a visit to Riyadh , General Dempsey urged Iraqi leaders to beware of what he called Iran's “nefarious” efforts to draw Iraq into its beliefs about world order and security. But, he said the United States also expects Iraq to have an economic relationship with Iran as the two nations are neighbors.

The quiet withdrawal was a sharp contrast to the start of the war in March 2003, when U.S.-led forces launched airstrikes over Baghdad as part of what they called a “shock and awe” campaign against Saddam. U.S. and allied ground forces then stormed from Kuwait into Iraq, toppling the minority Sunni dictator of a Shi'ite majority nation within weeks and capturing him by the end of the year.

Saddam's fall sparked a Sunni insurgency that evolved into a brutal sectarian conflict between Iraq's Shi'ite and Sunni communities, with violence peaking in 2006. The scale of sectarian and insurgent attacks declined significantly after 2007, when the United States sent a surge of troops to Iraq and Sunni tribal militias sided with U.S. forces against Sunni al-Qaida militants.

At the height of the war, more than 170,000 U.S. troops were stationed in Iraq at more than 500 bases. The United States promised to withdraw them by the end of 2011 under a 2008 U.S.-Iraqi agreement signed by the administration of former U.S. President George W. Bush and implemented by current President Barack Obama.

Iraqis have expressed mixed feelings about the U.S. pullout. Many have celebrated the end of what they called an American occupation and a regaining of Iraq's sovereignty, while others have expressed gratitude for U.S. help in ousting Saddam and introducing democracy.

Many Iraqis also complain that their elected government has not done enough to rebuild the country's war-ravaged infrastructure. Another common concern is that the Iraqi government's delicate power-sharing arrangements may unravel in the absence of U.S. troops and re-ignite a sectarian conflict.

In the latest sign of strains within the Shi'ite-led government, Prime Minister Nouri al-Maliki sent a letter to parliament Sunday asking lawmakers to fire his Sunni deputy, Saleh al-Mutlaq. The deputy prime minister called Mr. Maliki a “dictator” in a recent interview.

Mutlaq is a member of parliament's Iraqiya bloc, a secular group that has the support of many Sunnis and joined a Maliki-led national unity government after an inconclusive 2010 election. Iraqiya said Saturday it will boycott the assembly in protest at Mr. Maliki's perceived centralization of decision-making.

In a television interview recorded Thursday with U.S. network ABC News, President Obama said the U.S. troop presence in Iraq “succeeded” in giving Iraqis a chance to build a successful future. Mr. Obama opposed the war when he ran for office and vowed to end it. Opinion polls have showed a majority of Americans believe the war went on too long.