WASHINGTON — Japan is expanding its East China Sea surveillance network around the disputed Senkaku Islands, and a new radar observation station is expected to go online on March 28.

"This is kind of a power vacuum area," said Col. Masashi Yamamoto, military attaché with the Japanese Embassy here. , said Thursday.

"Considering North Korean activities, and the frequent invasion of our territory by China around these islands, we think we need to beef up our intelligence capability so that Japan can react better."

The Senkakus, called the Diaoyu Islands by the Chinese, are a group of eight uninhabited islands and barren rocks claimed by both nations. The island group, located about 300 miles west of Okinawa, has been administered by Japan since 1895. The Chinese stake their claim based on the group's location near Taiwan, traditionally a part of China. The islands have become increasingly significant due to their location near rich fishing grounds, shipping lanes, and potential oil and gas reserves.

Yamamoto noted that Chinese ships have sometimes crossed the 12-nautical-mile territorial limit around the Senkakus, and often have come within a 200-nautical-mile economic zone.

"Chinese Coast Guard ships continually enter the waters around the Senkakus," he said. "We think they are looking for a threshold to see what the limits are."

There is no indication, Yamamoto said, that Chinese naval or Coast Guard forces have come ashore on the Senkakus. "But ‘fishermen’ have landed," he said, referring to reported activists that have visited the islands. Chinese government militia that sometimes often pose as commercial seamen or fishermen could also come ashore, he added.

The new observation station is located on Yonaguni Island, about 90 miles east of Taiwan and south of the Senkakus. The radar and optical sensors on Yonaguni will extend by about 200 miles a Japanese observation network that stretches from the southernmost main island of Kyushu to Okinawa to Miyako Island.

With a population of about 1,800 people, the 11-square-mile Yonaguni is the westernmost inhabited island of Japan, and is 67 miles from Taiwan.

The observation station will be manned by about 150 Japanese Ground Self-Defense Force (JGSDF) soldiers, Yamamoto said, adding that, other than hand-held self-defense weapons, Yonaguni is not being fortified. The installation being built there is permanent, he said, and includes a new barracks to house the soldiers.

Japan is also beefing up its forces in the Amami Islands between Okinawa and the home islands where, Yamamoto said, "in the near future we will have a 600-troop security force."

There is no move, he added, to put forces on the Senkaku Islands themselves.

"If we put forces on the Senkaku Islands it would escalate tension," Yamamoto said. "We don't want to escalate. But on Yonaguni there are 1,800 residents. Yonaguni extends the observation network watching the Senkakus."

The observation network, Yamamoto explained, is Phase Zero of a multistep Japanese response approved in 2013 to react if tensions continue to rise.

Phase One would be the establishment of a JGSDF rapid deployment regiment consisting of an infantry company, a mortar company and a mechanized company equipped with new maneuver combat vehicles.

Phase Two would be activated should the islands be seized by an enemy, Yamamoto said, and would see an amphibious brigade deployed on naval ships to retake the territory.

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