Seoul ( CNN ) -- South Korea demanded Tokyo withdraw a ban that asks Japanese diplomats to refrain from flying with Korean Air to protest a test flight above islets in the sea east of Korea that Japan claims is its territory . `` The government is taking this seriously , as the Japanese government in effect is placing sanctions on one of our private companies , '' the South Korean foreign ministry spokesman said in a briefing Thursday . The islets in the sea east of Korea , known as Dokdo in Korea and Takeshima in Japan , have been a prickly issue for the countries . Japan has long claimed the islets as its territory , but Seoul leaves no room for debate and says all Korean territory was returned after the country won independence from colonial rule by Japan in 1945 . The Japanese government has shown no intention of stepping down from its recent move . `` Because Korean Air did a domain invasion to our Takeshima clearly this time , we have expressed our strong intention regarding this problem with Korean Air , '' the Japanese deputy foreign minister said . South Korea said it will consider various measures if Tokyo does not withdraw the measure that goes into effect Thursday . Seoul expressed strong disappointment at the move , saying it should not have been made given the relationship between the two countries . Korean Air , the country 's largest airliner , carried out two test flights over Dokdo less than a month ago but did not comment on the Japanese government 's decision . South Korea views the islets as a source of national pride and has taken various measures to reassert its ownership . The land is largely uninhabited with only seven registered residents .
Japan asked diplomats to refrain from flying with Korean Air . The move is to protest a test flight above islets in the sea east of Korea . Japan claims it is its territory . Comment: