South Korea's ruling party chief said Monday he told U.S. government officials and congressional leaders that Japan should offer a candid apology for its wartime atrocities if the frayed relations between Seoul and Tokyo are to improve.

Rep. Kim Moo-sung, chairman of the Saenuri Party, said he also told U.S. officials and congressmen that it is unacceptable for Japanese Prime Minister Shinzo Abe to issue a statement backtracking from previous statements of apology.

"One of the things that U.S. officials have expressed great interest in was how we are going to handle relations with Japan.

They appeared to be trying to mediate as our relations with Japan are tense," Kim said during a meeting with South Korean correspondents in Washington.

"What I told them is that we can never forget the humiliation that we suffered during the colonial rule, but we would like to cooperate with Japan. Nonetheless, we cannot accept Prime Minister Abe making remarks hurting our national feelings," he said.

Kim said he asked U.S. officials and congressional leaders to persuade Abe to stop engaging in such remarks and acts.

"What I told them is that Prime Minister Abe should offer a candid apology to our people in order to create an atmosphere where we can discuss a forward-looking future. Then will everything be resolved," Kim said.

Kim has been on a nine-day visit to the U.S. that includes a series of meetings with U.S. government officials and congressional leaders, including Deputy Secretary of Defense Robert Work and Sen.

John McCain, chairman of the Senate Armed Forces Committee.

During the meeting with McCain, Kim stressed the importance of Japan making a sincere apology for its wartime atrocities, saying that Japan's perception of history has been an obstacle to security cooperation between South Korea, the U.S., and Japan.

McCain told Kim in response that he calls for a sincere apology whenever he meets with Japanese officials and he will continue to do so in the future, according to Rep. Kim Jong-hoon, who also attended the meeting. (Yonhap)