The U.S. ambassador to Seoul said Thursday Japan’s sexual enslavement of Korean women during World War II is “a grave human rights violation,” expressing hope for Tokyo to take steps to ease the pains of victims.

Sung Kim made the remarks at a forum hosted by the Kwanhun Club, a senior journalists’ association, in Seoul, echoing Foreign Minister Yun Byung-se’s criticism the previous day in Geneva of Japan’s attempts to deny its wartime atrocities.

“Yes, I agree (with Yun),” Kim said. “The comfort women issue, or the sex slavery issue, is a grave human rights violation.”

Historians say up to 200,000 women, mostly Koreans, were coerced into sexual slavery for Japanese soldiers during World War II. Japan ruled the Korean Peninsula as a colony from 1910-45.

Tokyo, however, has been trying to whitewash its history of the sexual atrocities, with the Shinzo Abe government vowing to re-examine a 1993 statement where the country acknowledged and apologized for its war crimes.

Stressing his own and his country’s understanding of “the pains of the surviving women,” the U.S. diplomat said, “We very much hope that the Japanese leadership addresses this important issue in a way that eases the pain of the victims.”

The soured Seoul-Tokyo relations “are not only bad for the two countries but harm the U.S. interests and the peace and stability of the whole region,” Kim said.

While guarding against any “mediating role” by the U.S., he said Washington can “encourage the leadership of the two countries to address the issue in a way that satisfies concerns and eases pain.”

“We very much hope that we can see some positive momentum in the relations between South Korea and Japan.”

South Korean Foreign Minister Yun delivered a tough message to Japan in his speech at the 25th regular session of the U.N. Human Rights Council, saying Japan has shown an attitude of “affronting humanity and disregarding the historical truth” and “challenging recommendations to Japan by U.N. mechanisms” by not repenting for its past behaviors.

Yun said taking the international stage to raise the comfort women issue was to raise awareness around the world and seek solutions to these “universal human rights issues.”

Asked about ways to resolve the North Korean nuclear weapons program, the U.S. diplomat said he believes that the six-party talks “are still a useful forum” and stressed Washington’s will to resume the stalled meeting.

The multilateral talks, which involve both Koreas, the U.S., Japan, China and Russia, have been dormant since late 2008.

“The North Korean nuclear issue is still very much at the top of the foreign policy of the U.S.,” the ambassador said. “People often equate lack of progress with lack of interests in Washington. That’s not the case at all in this case.”

Pointing to current circumstances as a reason for its “prudent” approach, he said the U.S. “will continue to work very hard with South Korea and China to try to come up with the resumption of the talks” with a goal to make “a serious lasting progress” in the denuclearization matter.

Especially following the stunning execution of leader Kim Jong-un’s uncle and No. 2 man, Jang Song-thaek, political uncertainty and instability in the reclusive country have grown, according to watchers.

“Many questions and many answers exist about the situation in North Korea. This is why it is so critical, so important for us to continue to maintain the strongest possible deterrent capability so that we will be prepared for whatever happens in North Korea,” he said.