Japan's Osaka Mayor Toru Hashimoto continues to strain tensions between Seoul and Tokyo, issuing another controversial remark Monday about Japan's wartime sex slavery.

The co-leader of the conservative Japan Restoration Party said at a news conference for foreign correspondents that the issue of compensation for wartime sex slaves was settled through the Treaty on Basic Relations between Japan and the Republic of Korea signed in 1965.

He said if South Korea can't accept that, the Seoul government can file a suit with the International Court of Justice.

Hashimoto added that the Japanese government was never involved in organized kidnapping and human trafficking, raising a question on reliability of victims’ testimony.

However, Hashimoto did apologize to the United States in the statement.

He said his remark urging U.S. troops stationed in Okinawa to make use of brothels was inappropriate as American servicemen and the American people could have felt insulted. He said he withdraws the remark and is sorry.