LONDON – Japan ordered the withdrawal of its 600 troops from Iraq yesterday after declaring that the mission – which stretched the country’s pacifist constitution to the limit – had been a success.

The withdrawal was announced by Prime Minister Koizumi a day after Britain said it would hand over control of Muthanna province, where the Japanese troops have been deployed, to Iraqi security forces.

It follows a decision by Italy to bring home its troops in the coming months and by South Korea to reduce its contingent.

The Iraqi foreign minister, Hoshyar Zebari, expressed confidence that departing coalition troops would not leave a security “vacuum.”

Following talks in London with Margaret Beckett, the British foreign secretary, Mr. Zebari confirmed that Maysan province, which shares a border with Iran, will be taken over by Iraqi forces next.

Mrs. Beckett would not say whether the 800 British soldiers in Maysan would return home or be redeployed to other parts of Iraq.

Describing the handover of Muthanna as a milestone, she predicted that “we will see more provinces handed over as they meet the necessary security conditions over the next 12 to 18 months.”

The Japanese contingent was a non-combat unit on a reconstruction mission. Its protection had to be provided by British and Australian troops.

Nevertheless it marked a step in Japan’s abandonment of its postwar pacifist doctrine.