President Yoon Suk Yeol arrived Monday evening in Vilnius, beginning a six-day trip to Lithuania and Poland to discuss an array of issues including military cooperation, North Korea's nuclear deterrence measures and the controversial discharge of contaminated wastewater from the wrecked Fukushima nuclear power plant in Japan.

Attending a North Atlantic Treaty Organization summit for the second time, the South Korean leader will be seeking measures with member countries to bolster cooperation in countering Pyongyang's evolving nuclear weapon threat, the ongoing war in Ukraine and regional security in the Indo-Pacific.

On the sidelines of the summit, Yoon is expected to meet his Japanese counterpart amid strong resistance building in South Korea over the Japanese government's plan to release treated radioactive wastewater from the destroyed Fukushima Daiichi Nuclear Plant, despite the International Atomic Energy Agency's final assessment last week that gave a green light to the plan.

Prime Minister Fumio Kishida is expected to detail Japan's imminent discharge plan, safety considerations and future self-monitoring strategies to Yoon. The presidential office stated that the government's fundamental stance on the release of the wastewater prioritizes the health and safety of the people, and this position will be clearly conveyed.

However, as the Korean government said it "respects" the IAEA's report, it seems unlikely that new disagreement will emerge during the Korea-Japan summit.

Accompanied by a business delegation in Poland, Yoon is expected to participate in discussions intended to boost cooperation in strategic sectors such as defense, nuclear power and infrastructure. First lady Kim Keon Hee is accompanying him.

Yoon, who is attending the NATO summit for a second time as an observer, he is likely to urge the international community to raise a united voice that it will not tolerate illegal activities such as North Korea's threats of developing nuclear weapons.

In an interview with AP released on the day of his departure for Vilnius, Yoon said now is the time to clearly demonstrate that the international community’s determination to deter North Korea’s nuclear weapons program is “stronger than” North Korea’s desire to develop nuclear weapons.

While at the summit, Yoon is scheduled to meet with NATO Secretary-General Jens Stoltenberg and leaders of Asia-Pacific nations, including Australia, Japan and New Zealand. He will also hold multiple bilateral meetings with leaders from Norway, the Netherlands, New Zealand, Hungary, Romania, Sweden, Estonia, Slovakia, Finland and Lithuania.

Yoon intends to adopt bilateral cooperation documents between Korea and NATO in 11 sectors -- including cybersecurity and emerging technologies -- at this summit, according to his office.

After concluding his activities in Lithuania, Yoon will travel to Warsaw, Poland for an official visit at the invitation of Polish President Andrzej Duda. Yoon is the first South Korean leader to visit the European country in 14 years since former President Lee Myung-bak's trip to the nation in 2009.

The two leaders are expected to discuss the advancement of the strategic partnership between the two countries, which celebrates its 10th anniversary this year.

During his visit to Poland, Yoon is anticipated to engage in discussions aimed at bolstering cooperation in strategic sectors like defense, nuclear power and infrastructure. Additionally, they will discuss potential collaboration on reconstruction efforts in Ukraine.

Several other events are on Yoon's itinerary, including a business forum attended by leaders from both countries, an interaction with young South Korean and Polish individuals at the University of Warsaw and a meeting with Korean residents of Poland.

Yoon will be accompanied with a delegation of Korean business leaders including LG Group Chairman Koo Kwang-mo, Hanwha Group Vice Chairman Kim Dong-kwan and Daewoo Engineering and Construction Chairman Jung Won-ju.

Meanwhile, Yoon’s approval rating for state affairs dropped back into the 30 percent range after three weeks of steady growth. According to a survey conducted by Realmeter and commissioned by Media Tribune, 39.1 percent of respondents evaluated his performance positively, a decrease of 2.9 percentage points from the previous week. Negative evaluations increased to 58 percent, up by 2.9 percentage points, reversing a three-week decline.