Moon is widely expected to seek ways to mend fences with Japan as part of parliamentary diplomacy.

He plans to deliver a keynote speech in the G-20 meeting Monday, stressing the need to promote free and fair trade.

Moon reportedly has a plan to elicit support from the participating countries over key contentious issues between Seoul and Tokyo by indirectly mentioning the unjustness of Japan's trade restriction measures.

But reflecting the chilly bilateral ties, Moon's parliamentary diplomacy appears to face challenges as his proposed meetings with Japanese lawmakers remain uncertain.

Akiko Santo, president of the House of Councilors, is refusing to meet with Moon, citing his previous remarks over Japan's wartime sexual enslavement of Korean women.

In an interview with Bloomberg in February, Moon raised the need for the outgoing Japanese emperor to make an apology over Japan's sexual slavery issue.

Moon made his third apology over his remarks during his recent interview with Japan's Asahi Shimbun, in an apparent bid to ease negative public sentiment in Japan.

On Tuesday, the speaker will visit Waseda University to give a lecture on ways to restore relations between South Korea and Japan. (Yonhap)