Japan, a close Washington ally, backed the US-led invasion of Iraq and provided ground troops for a non-combat, humanitarian mission in the southern Iraqi city of Samawah in 2004.
It withdrew ground troops in July 2006, and has since expanded its Kuwait-based air operations.
The Iraq mission is part of Japan's bid to boost its international profile.
In October, Tokyo approved a one-year extension of its naval mission in the Indian ocean to support US-led troops in Afghanistan.
Critics say the operations violated the country's pacifist constitution which prohibits the use of force in settling international disputes.