The U.S. military handed over its last base in Iraq to the Iraqi authorities on Friday, a day after the U.S. force marked the end of its mission in the country, as the remaining 4,000 U.S. soldiers are moving out on a daily basis.

The transfer ceremony was held at the Imam Ali Base in the outskirts of the southern city of Nasiriyah. U.S. Col. Richard Kaiser, commander of the base, and Hussein al-Assadi, representative of Iraqi Prime Minister Nouri al-Maliki, signed over at the ceremony.

"We proudly announce to the Iraqi people today the handover of the last American military base," Assadi told reporters after the signing, adding that "Today we are turning the last page on the occupation."

Friday's handover came after U.S. Defense Secretary Leon Panetta announced the end of the U.S. military mission in Iraq Thursday near the Baghdad International Airport.

Some 4,000 soldiers remain in Iraq, down from a peak of nearly 170,000 troops and 505 bases across the country. Most of the remaining troops are to depart before the Dec. 31 pullout deadline.

The U.S. embassy, in the wake of the withdrawal, will retain 157 U.S. soldiers for the training of Iraqi forces, and another team of U.S. marines to guard the diplomatic mission.

The Imam Ali Base, occupying 30 square kilometers and being protected by 22 kilometers of security perimeter, was built in the 1980s by former Iraqi president Saddam Houssein and taken over by the U.S. force after the start of the 2003 invasion.

The base, which the U.S. military brands as Camp Adder, housed 15,000 American troops at the height. Units of the U.S. Army, the Air Force, the Navy, and the Marine Corps have since been stationed at the base. The airfield of the base is featured with two main runways and a modern air traffic control tower, which was built in March 2010.

The transfer of the base took place at the conclusion of a war which claimed lives of hundreds of thousands of Iraqis and nearly 4,500 U.S. soldiers and marked the end of nearly nine years of the U.S. military involvement in Iraq that started in 2003 and toppled Saddam's regime.

Sectarian conflicts have been increasing after the invasion, between the country's minority but elite Sunni Arabs and the majority Shiite tribes. Brutal bloodshed was triggered by the bombing of a Shiite shrine in the Sunni-dominated city of Samarra by the al-Qaida in February 2006.

Sporadic attacks are still common in Iraqi cities despite the dramatic decrease of violence over the past few years.

"Iraq will be tested in the days ahead by terrorism and by those who would seek to divide it, by economic and social issues, by the demands of democracy itself," said Panetta, at Thursday's symbolic flag-lowering ceremony in Baghdad.

Iraqi Prime Minister Nouri al-Maliki said the country's 77,000- strong army force is ready to fully take security responsibility.