The Japanese government reportedly summoned the South Korean ambassador to Tokyo on Thursday to lodge a protest against a Seoul court’s ruling in favor of victims of Japan’s wartime sexual slavery.

According to Japan’s public broadcaster NHK and Kyodo News, Japan’s vice foreign minister Masataka Okano summoned South Korean Ambassador Yun Duk-min to convey Tokyo’s dismay, calling the ruling “extremely regrettable.”

The Seoul High Court on Thursday ordered Japan to compensate a group of victims of wartime sexual slavery, overturning a lower court ruling that dismissed the case.

The Japanese vice foreign minister said that the ruling failed to apply the “state immunity” concept of international law preventing an impingement on sovereignty in litigation, calling it very regrettable and absolutely unacceptable.

Okano then asked the Seoul government to produce proper measures to rectify the violation of the legal concept.