Japanese troops crossed Sunday into Iraq (search) from Kuwait, beginning the country's first deployment to a combat zone since 1945.

The troops, most of them engineers, are spearheading a deployment of about 800 troops in a humanitarian mission in southern Iraq.

They traveled in a 25-vehicle convoy from the U.S. Camp Virginia (searchin the Kuwaiti desert to the border. The convoy included armored vehicles, trucks, personnel carriers, and an ambulance.

The number of the soldiers in the convoy was not disclosed.

Japan has already dispatched advance teams and three C-130 cargo planes to the region. The troops will purify water and carry out other humanitarian tasks in Iraq.

The deployment to Iraq is Japan's largest and riskiest since World War II (search). It has faced strong opposition at home amid fears for their safety with the insurgency in Iraq.

The mission is the first time Japanese troops have gone to a combat zone since 1945. While Tokyo has sent soldiers on peacekeeping missions in the past, they have only gone to areas where fighting has subsided.

Japan's constitution, adopted in 1947 during the U.S. postwar occupation of the country, renounces the use of military force.

The decision by the government of Prime Minister Junichiro Koizumi (searchto deploy the troops despite widespread opposition reflects a shift in the government's attitude since the 1991 Gulf War, when Tokyo shouldered a portion of the financial burden but sent no soldiers.

Koizumi and his allies in the ruling Liberal Democratic Party have been eager to contribute Japanese troops to back the United States, its most important ally.