The former head of South Korea's largest opposition party has said his country needs to promote economic and other forms of cooperation with Japan.



Lee Jae-myung stepped down as leader of the Democratic Party last week before announcing his candidacy in South Korea's presidential election in June.
Polls show him to be the frontrunner in the race.



Lee referred to relations with Japan in a video message he posted on Tuesday.



He said he is very critical of Japan's words and actions, but from a broader view the two countries must cooperate. If not, both sides would suffer.



Lee also referred to the Takeshima Islands in the Sea of Japan, which South Korea calls Dokdo.



South Korea controls the islands. Japan claims them. The Japanese government maintains the islands are an inherent part of Japan's territory. It says South Korea is illegally occupying them.



Lee said the two countries have disputes over Dokdo and historical issues, but that economic, cultural and social aspects should be free of such dissension.



Regarding North Korea, Lee said the country deepened cooperation with Russia because the administration of former South Korean President Yoon Suk-yeol took a tough stance toward Pyongyang. He said Seoul must improve relations with its northern neighbor.