Korean Air recently ran a demonstration flight of its new Airbus A380 aircraft over the disputed Dokdo islands (AFP/File, Eric Piermont)

South Korea's prime minister urged Japan Tuesday to drop its boycott of a Korean airline which flew over islands claimed by both nations, calling the ban a breach of international rules.

Kim Hwang-Sik also protested against a plan by Tokyo lawmakers to visit the closest point to the disputed Dokdo islands which are controlled by South Korea, calling it "very regrettable".

The latest flare-up in the decades-old dispute came when Korean Air operated a demonstration flight of its new Airbus A380 aircraft in June over the Dokdo islands, which are known as Takeshima in Japan.

Tokyo in response ordered civil servants not to use Korean Air for one month.

"A move targeting a private firm like Korean Air is inappropriate and may contravene global diplomatic protocols and WTO (World Trade Organisation) rules," Kim's spokesman quoted him as saying in a cabinet meeting.

Kim demanded the airline boycott be ended immediately, saying it was an "unchanging truth" that the rocky islets in the Sea of Japan (East Sea) belong to South Korea.

Four lawmakers from Japan's conservative opposition Liberal Democratic Party last Friday announced plans to visit Ulleung island -- the closest South Korean territory to Dokdo -- next month.

The move drew anger from Seoul lawmakers, one of whom pledged to "stop the entry to Ulleung island by all possible means".

"If the visit is aimed to reassert a territorial claim on Dokdo... I want them to get real and cancel the trip immediately," Special Affairs Minister Lee Jae-Oh wrote on his Twitter account on Saturday.

South Korea, which was colonised by Japan from 1910-1945, has sought to strengthen its control over the islets after Japan in March authorised new school textbooks reasserting its claims to them.