The Defense Agency would deploy 7,200 ground troops to protect Japan's southernmost islands from invading Chinese forces in the event of a conflict between China and Taiwan, according to confidential documents obtained by Kyodo News.

It is the first time internal agency documents have been found to assume that China might attack Japanese territory.

The agency's Ground Staff Office believes China might invade the remote islands in Okinawa Prefecture to block joint support operations for Taiwan by Japan and the United States, according to the documents obtained Thursday.

Military experts believe the office is trying to emphasize the importance of the Ground Self-Defense Force by identifying the "new threat" of a possible Chinese invasion, because the agency will soon compile its next defense plan guideline and is expected to restructure the Self-Defense Forces.

But the experts called the scenario unrealistic, saying it was a "made-up threat." It is unlikely that China would choose the highly risky option of engaging in war on two fronts, against Taiwan as well as against Japan and the United States, they said.

Sources said the documents were compiled by the Ground Staff Office in November as part of operations to revise the defense guidelines.

Amid budget cuts on tanks and artillery to make way for an expensive missile defense system after the end of the Cold War, the GSDF is trying to shift its focus to the west from the north, given the current security tensions over the Korean Peninsula and the Taiwan Strait.

"It is unrealistic and difficult to imagine that the Chinese army would really invade the Japanese islands, although it is possible Japan would be affected by a conflict between Taiwan and China," said Tetsuo Maeda, a national security professor at Tokyo International University.

"It is better to see this as the GSDF trying to stress its new role under new threats," Maeda said.

The countries concerned were not named in the documents. China was referred to as X and Taiwan as D.

The three southern islands targeted for invasion under the assumption are Miyako Island, Ishigaki Island and Yonaguni Island, according to the documents.

The documents reckon Miyako and nearby islands are likely to be targeted because an Air Self-Defense Force radar base and two airports are located in the area.

The office assumes China might invade Yonaguni Island, the westernmost part of Japan and 100 km from Taiwan, as a stepping stone to attack Taiwan.

It also assumes that China would attack the islands by sea and air, with marine forces landing from assault ships as well as airborne units and special forces attacking ASDF bases and airports, the documents show.

The office figures China would deploy 1,400 troops to attack Miyako and Yonaguni islands. If Ishigaki Island is included, the number would total 5,200, the documents say.