President Yoon Suk Yeol (left) and Japanese Prime Minister Fumio Kishida hold a summit at the Japanese Prime Minister's Office in Tokyo, Japan on March 16. (File Photo - Office of the President)

South Korean President Yoon Suk Yeol will embark on a six-day trip Monday to attend the NATO summit in Lithuania and visit Poland, but the focus will be on his meeting with the Japanese leader, where the two are expected to discuss Tokyo's plan to release treated wastewater into the sea.

The South Korean presidential office confirmed Sunday that the summit between Yoon and Japanese Prime Minister Fumio Kishida will take place on the sidelines of the NATO Vilnius Summit on Tuesday and Wednesday. Both countries have been invited to the summit as two of NATO's four Asia-Pacific partners, also known as AP4, along with Australia and New Zealand.

The Yoon-Kishida summit comes at a critical juncture, as Yoon's political opponents have launched an aggressive campaign against Japan's wastewater release plan. They have also publicly accused the UN's nuclear watchdog of pro-Japanese bias, citing its final safety assessment that gave the green light to Tokyo's proposal to discharge more than a million metric tons of treated wastewater into the Pacific Ocean.

The presidential office suggested that Japan's planned water discharge, widely expected to begin in August, will be a major topic on the agenda of the summit between Yoon and Kishida.

"We will unequivocally convey our position on the issue raised by the Japanese side under the principle of prioritizing the health and safety of our citizens," a senior presidential official, who wished to remain anonymous, said Sunday, when asked how Yoon would respond if Kishida asks for understanding of the discharge of treated radioactive water.

Observers also say Kishida could repeat his request to lift South Korea's bans on marine products from Fukushima and seven other nearby prefectures. But Seoul has said it will not lift the ban unless Tokyo provides scientific evidence that the seafood is safe.

The unnamed official explained that Seoul and Tokyo have been in discussions on the format and timing of the summit. But the forthcoming meeting might be slightly shorter that previous ones because Yoon's schedule during the two-day NATO summit also includes over 10 separate bilateral meetings, as well as the quadripartite summit of AP4 countries.

The Yoon-Kishida summit, the first since May and the fourth this year, will occur amid intense debate in South Korea that has intensified amid the three-day visit of IAEA Director General Rafael Mariano Grossi to Seoul.

Grossi's trip followed the IAEA's announcement of a report concluding that the discharge of treated water from Fukushima would have a minimal radiological impact on people and the environment.

The South Korean government on Friday released a report concluding that Japan's proposed plan to release treated wastewater from the Fukushima nuclear plant into the Pacific Ocean "would meet international standards if implemented as planned." But it emphasized that the report only pertained to the scientific and technological analysis of the water's release.

The government has reiterated that it will not detail its official position on the pros and cons of the wastewater release until Japan announces its definite, finalized plan for the release of contaminated water, leaving room for further discussion.

South Korea's Foreign Ministry on Sunday said it will continue to pursue further discussions with Japan through appropriate channels and methods before Japan finalizes its plan for water discharge.

The foreign ministers of South Korea and Japan are widely expected to engage in separate talks later in the week, which presents another opportunity for South Korea to voice its concerns and position on the issue.

South Korean Foreign Minister Park Jin and his Japanese counterpart Yoshimasa Hayashi will participate in the ASEAN Ministers Meeting and other related regional meetings in Jakarta on Thursday and Friday.

If one-on-one foreign ministerial talks take place on the sidelines of the ASEAN meeting, Japan's water discharge will be among the key topics of discussion, South Korea's Foreign Ministry has stated.