South Korea's military had set a guideline in February 2019 on what kind of situation to lock its fire-control radar on a Japanese Self-Defense Forces patrol plane, two months after it carried out the move, a lawmaker said Friday.

Relations between South Korea and Japan — U.S. security allies in the region — sharply deteriorated against a backdrop of the radar irradiation, along with unresolved historical grievances, Tokyo's imposition of export control measures and other disputes.

The revelation indicates that the administration of South Korea's president at the time, Moon Jae-in — known as an anti-Japan politician — had decided early on a hard-line approach to Tokyo, with bilateral distrust growing in several fields, including defense.

The guideline has instructed the South Korean navy to direct its fire-control radar at a Japanese maritime patrol aircraft if the plane does not respond to two warnings by the nation's military vessels when it approaches them, the lawmaker said.

In December 2018, Japan said a South Korean navy destroyer had locked its fire-control radar on the SDF patrol aircraft. Seoul denied it and alleged that the Japanese plane deliberately flew at low altitudes near the South Korean naval ships three times.

Shin Won-sik, the lawmaker who belongs to the defense committee at the parliament, said the guideline only targets Japan's SDF, while calling it "very dangerous."

The South Korean Defense Ministry has told him that it is considering whether to abandon the guideline, said Shin, a member of the ruling People Power Party. Moon was replaced in May by President Yoon Suk-yeol, who has voiced a willingness to improve ties with Japan.