Junichiro Koizumi, the Japanese Prime Minister and architect of a growing international assertiveness, said: “The Ground Self-Defence Force has played a considerable role in providing humanitarian reconstruction assistance and we have decided to withdraw." All off the troops are expected to be back in Japan by mid-July.

However, in a sign of growing military boldness, Japan will expand the mission of its Air Self-Defence Force from its present role of providing transport between Kuwait and Samawah, southern Iraq. Japan will commit its fixed-wing aircraft and helicopters to the risky task of airlifting United Nations personnel and multinational troops in and out of Baghdad. Mr Koizumi, who will travel to Washington this month for a meeting with President Bush, was directly asked by the United States to deploy air personnel in that role.

Mr Koizumi said that “a chapter has been finished”. It is also certain that a new chapter has begun. Although Japanese troops have spent 2½ in the southern city of Samawah in a non-combat reconstruction role, their presence in a war zone marks a critical psychological turning point for Japan.

The mission to Iraq required a clause of the pacifist Japanese Constitution to be stretched to its limit and a controversial military dispatch law to be hurried through parliament. The deployment placed Japanese forces in harm’s way for the first time since the end of the Second World War.

The Government is preparing legislation that would upgrade the Defence Agency to a full ministry, which might eventually lead to the country’s euphemistically named Ground Self-Defence Force (GSDF) assuming the more accurate title of “army”.

This year Japan created the military role of Chief of the Joint Staff Office. General Hajime Massaki, the holder, told The Times that the military forces stand ready for international dispatch in a variety of roles.

Japan’s decision to withdraw its troops follows consultation with the US, Britain and Australia. British and Australian troops have protected Japanese GSDF forces during their time in Iraq, allowing them to adhere to a non-combat role. Security duties in Musanna province will be transferred to Iraqi control over the summer.

Although Mr Koizumi said today that GSDF troops had undertaken considerable reconstruction of Iraqi infrastructure since January 2004, few Japanese have bothered to keep abreast of their troops’ activities. Newspaper polls regularly indicate that a majority of Japanese oppose the overseas posting of troops, with many believing that it represents a clear breach of the 1947 Constitution.

Seven Japanese civilians have been kidnapped and five killed in Iraq since the war began in 2003. The loudest public calls for the GSDF troops to return came shortly after their mission began, when three Japanese aid workers were held hostage in Iraq with demands that Mr Koizumi withdraw troops.

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