Japan has lodged a formal protest against a Seoul court ruling on Friday that ordered the compensation of Korean victims of the Japanese military's sexual enslavement of women during World War Two.

Japan's Foreign Ministry summoned South Korean Ambassador Nam Kwan-pyo and Vice Foreign Minister Takeo Akiba expressed deep regret, claiming that the South Korean court denied the principle of state immunity, stressing that Tokyo cannot accept it.

At a press conference, Japan's Chief Cabinet Secretary Katsunobu Kato reiterated Tokyo's position that the sexual slavery issue was resolved through the 1965 treaty that normalized bilateral ties as well as a bilateral settlement agreement in 2015.

Kato said Tokyo will demand Seoul take steps to correct its international law violations. The country, however, will not appeal Friday's ruling in accordance with the principle of state immunity.

Japanese media outlets expected that two-way ties, aggravated by Japan's wartime forced labor issue and retaliatory export curbs, might take a turn for the worse as the latest ruling could result in Seoul seizing Tokyo's assets in South Korea.