"One part will leave tomorrow," the prime minister's spokesman Yu Kameoka said, without specifying the size of the detachment, or the branch of the armed forces they are drawn from.
A 40-strong advance party of airforce servicemen would leave for Kuwait to prepare for the dispatch of 150 other airforce members in January, according to the online edition of the Yomiuri Shimbun daily.
The dispatch is part of Japan's plan to deploy a total of about 1000 troops to the region for humanitarian and reconstruction work in Iraq.
After months of foot-dragging, Prime Minister Junichiro Koizumi's cabinet formally decided on 9 December to send a maximum of 600 ground troops to Iraq on a mission to last until December next year.
It is the first time that a Japanese military unit will be sent to a country where fighting is still raging. Japan's post-war constitution bans the use of force in settling international disputes.
The deployment plan has provoked strong opposition at home and has aroused fears among neighbouring nations about Japan's militarist revival.
About 1500 people gathered at Tokyo's Harumi harbour to see off 520 activists who boarded a chartered cruise liner with the banner "Don't send soldiers" at the start of a protest cruise to Okinawa.
"A majority of Japanese people are opposed to the dispatch of
Japan's Self-Defence Forces to Iraq. If we are really a democratic country, I think the government should consider that," Tatsuya Yoshioka, director of the Peace Boat activist group, which organised the trip said, arguing the move contravenes Japan's pacifist constitution.
Two newspaper polls released earlier this week found that 52% of Japanese are opposed to the troop dispatch.
"A majority of Japanese people are opposed to the dispatch of troops to Iraq. If we are really a democratic country, I think the government should consider that"
Director of Peace Boat
With concerns persisting that Japanese troops may be targeted for attack, Koizumi was due to give an interview on Thursday to Aljazeera channel to explain the rationale behind the deployment plan.
Defence Agency chief Shigeru Ishiba told Aljazeera earlier in the day that Japan's planned deployment was aimed at helping Iraqis set up their own government, Kyodo News reported.
Meanwhile, Koizumi's ruling Liberal Democratic Party's coalition
partner, New Komei Party, was treading cautiously on Thursday, with lawmakers reserving a decision to support the dispatch of ground forces to Samawa in southern Iraq until a later date.
"There is still time before a ground forces dispatch," said New Komei spokesman Masayuki Kato. "So lawmakers said they wanted to gather again and have that chance to talk about it."
On Wednesday, Koizumi warned of the danger facing Japanese troops in Iraq at a send-off ceremony for some of those bound for the war-torn country on Japan's most risky military mission since World War II.