The move to withdraw followed the announcement on Monday that Britain and Australia would hand over responsibility for security to Iraqi forces in southern Muthana province, where the Japanese troops are based.

That apparently was the signal to Tokyo that is was time to go. Japan has been concerned that its troops could be drawn into the fighting in Iraq.

Nukaga ordered the withdrawal to begin later Tuesday. The Yomiuri newspaper reported the target for completing the pullout was the end of July.

Polls showed half or more of the Japanese public opposed the mission, and many were concerned about the safety of troops in Iraq and the possibility that the dispatch would make Japan a target of terrorists.

Critics also said the dispatch violated the U.S.-drafted 1947 constitution, which foreswears the use of force to settle international disputes. The Iraq mission followed a dispatch of Japanese ships to offer logistical support for military action in Afghanistan.

Koizumi defended the deployment on Tuesday.

"I believe we made the right decision," he said.

While no Japanese soldiers suffered casualties, other citizens in Iraq were targeted by militants demanding a Japanese withdrawal. Seven Japanese have been kidnapped in Iraq since the deployment, and two of them were killed.

Japanese backpacker Shosei Koda, 24, was kidnapped and decapitated in Iraq in October 2004. Militants claimed to have abducted Akihito Saito, 44, a Japanese security manager employed by the British company Hart GMSSCO. A later statement said he died of wounds suffered in an ambush.

Throughout, Koizumi was steadfast in his insistence on continuing the dispatch, despite polls that showed most Japanese were against it.

The harshest test of the policy came in April 2004, when three Japanese aid workers were kidnapped and threatened with death unless Tokyo withdrew. Koizumi refused, and all three were later released unharmed.

Still, opposition to the dispatch was strong. A poll published in the national Asahi newspaper late last year showed 69 percent of respondents opposed to continuing the mission. Nevertheless, Japan's government in December extended the dispatch for another year.