Japan's foreign ministry has ordered a one-month boycott of Korean Air to protest a demonstration flight by the airline that passed over islands claimed by both countries.

Officials said Thursday that Japanese diplomats have been ordered not to use the Korean airline for the next 30 days. In addition, KAL officials will not be invited to any events hosted by the ministry.

South Korean officials immediately protested the action, calling it unacceptable. They demanded that Japan immediately withdraw the ban.

Japan is protesting a June 16 flight in which KAL demonstrated its first Airbus super-jumbo A380 for a group of business executives and journalists. The plane recently went into service between Seoul and Tokyo.

Japanese officials say the plane violated Japanese air space when it flew over a group of rocky islets known in South Korea as Dokdo and in Japan as Takeshima.

The islands, with only a handful of permanent inhabitants, are effectively administered by South Korea, which reclaimed them after emerging from Japanese colonial rule in 1945.

South Korea's Chosun newspaper reported Thursday that the nation's military is expanding an air base in the Sea of Japan to boost its defense of the islands, also known as the Liancourt Rocks. South Korea calls the surrounding body of water the East Sea.