Japan ordered the withdrawal of its ground troops from Iraq on Tuesday, declaring the humanitarian mission a success and ending a groundbreaking dispatch that tested the limits of its pacifist postwar constitution. Prime Minister Junichiro Koizumi said the 600 non-combat troops - deployed in early 2004 - had helped rebuild the infrastructure of the area where they were based, and he pledged further aid to Iraqi reconstruction. "Today we have decided to withdraw Ground Self-Defense Forces from the Samawah region in Iraq," Koizumi said in a nationally televised news conference. "The humanitarian dispatch ... has achieved its mission." The withdrawal was decided in consultation with the United States and other allies, Koizumi said. Defense chief Fukushiro Nukaga told reporters earlier in the day that the pullout would take "several dozen days." Koizumi has been a vocal supporter of US policy in Iraq, arguing that the dispatch was needed to aid reconstruction, secure oil supplies and bolster ties with Washington. He is to travel to Washington for a summit with President George W. Bush the last week in June, before stepping down in September. Japan, which hosts 50,000 US troops under a security treaty, will continue to stand with Washington, Koizumi said. "Japan's policy to cooperate with the United States based on the importance of the Japan-US alliance has never changed and will not change," he said. The dispatch constituted Japan's largest and most dangerous overseas military mission since the end of World War II. While concerns for troop safety were high, the region they were based in was relatively peaceful. As security deteriorated, they were largely confined to their base. Tokyo will now consider expanding Air Self-Defense operations in Iraq to include transport of medical supplies and UN personnel, following a request from UN General-Secretary Kofi Annan, said Takenori Kanzaki, head of the ruling party's coalition partner, the New Komei Party. "Even after the withdrawal from Iraq, we must continue the efforts to support Iraq," Kanzaki told reporters. Japan has about 600 troops in the city of Samawah in southern Iraq. Although the mission is strictly non-combat and humanitarian, the deployment in early 2004 broke new ground as a symbol of Tokyo's more assertive military policy. 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. Concerns have been high in Japan that the troops could be drawn into the fighting in Iraq, and the shift in security responsibility was apparently being taken as a chance by Tokyo to withdraw. Nukaga issued an order for 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 dispatch, 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 US-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 dispatch, 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.