South Korean troops are leaving Iraq, bringing to an end a mission that focused on rebuilding hospitals, roads and schools but which divided South Korea's people.

Some South Koreans believed participating in the Iraq operation would strengthen ties to the United States. Critics argued the mission was part of an unjustified war.

The departure of the "Zaytun" contingent — the Arabic word for olive and the troops' codename for their mission — is the latest exodus from dwindling U.S.-led coalition. The South Koreans are among troops from 13 countries being sent home in advance of the Dec. 31 expiration of the U.N. mandate that authorized military operations in Iraq.

A ceremony to mark the end of the mission was scheduled Monday in Irbil, the capital of the Kurdish self-ruled region 220 miles north of Baghdad.

At its height, the coalition numbered about 300,000 soldiers from 38 countries — 250,000 from the United States, about 40,000 from Britain, and the rest ranging from 2,000 Australians to 70 Albanians.

As the war continued and the insurgent violence increased, the coalition dwindled as countries either reduced their contingents or pulled their troops completely.

Already Armenia, Georgia, Kazakhstan, Latvia, Macedonia and Bosnia-Herzegovinia have recently ended missions in Iraq. Other countries were set to follow later this week.

The only remaining coalition troops to remain in Iraq after the mandate expires will be the U.S.'s biggest ally, Britain, as well as Australia, El Salvador, Estonia and Romania.

"The composition of the coalition will change significantly between now and the end of the year as (the mandate) expires and will be based on decisions made by the government of Iraq and coalition members," said Col. Bill Buckner, a U.S. military spokesman.

Iraq's parliament has approved a U.S. security pact that requires all American troops to withdraw from the country in three years. The pact still must be signed by a three-member presidential council and submitted to the voters in a referendum by July 31.

Buckner said those countries whose troops remain in Iraq will negotiate their own agreements with the Iraqi government.

Additionally, he said coalition forces will reassess battlefield operations as the Iraqi security forces improve and the threat levels decrease.

South Korea has had troops stationed in Iraq as part of a reconstruction mission since 2003 at the request of Washington, which has 28,000 troops based in South Korea as deterrent against North Korea.

Technically, the two Koreas are still at war, because their 1950-53 Korean War ended in an armistice, not a peace treaty.

The deployment has been unpopular among some South Koreans, who generally view the U.S.-led war in Iraq as unjust. South Korea's government had to overcome strong protests from activists when accepting U.S. requests for troops and later to extend the deployment.

Opposition mounted after Islamic extremists beheaded a South Korean civilian working in Iraq in 2004.

South Korea's troop level once stood at 3,600. But the government gradually reduced the number because of anti-war sentiments.

As of December 2007, South Korea had about 650 troops in Iraq.

The U.S. has more than 150,000 troops in Iraq, compared with 4,000 for Britain, the second largest contributor.