TOKYO — Japan has doubled the number of F-15 fighter jets deployed on the southern island of Okinawa, near disputed islands in the East China Sea, the Defense Ministry said Sunday.

Japan’s Air Self-Defense Force now has about 40 F-15s on Okinawa’s Naha base, according to the Defense Ministry.

The move comes as Japan and China have routinely clashed over ownership of the Tokyo-controlled Senkaku Islands in the East China Sea.

Japan administers the uninhabited islands under that name but China also claims them and calls them the Diaoyus.

Chinese ships — mostly coast guard vessels — and aircraft have approached them to back up Beijing’s claims and test Japan’s response.

“This is a very front line of national defense,” said Deputy Defense Minister Kenji Wakamiya, quoted by Jiji Press, at the Sunday ceremony at the Naha base to mark the creation of a new unit composed of the extra jets.

The Defense Ministry moved about 20 F-15s from the Tsuiki base in the southwestern island of Kyushu to Naha, the Defense Ministry said.

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