Lawmakers from South Korea's opposition flew to Japan on Monday to join forces with their Japanese counterparts in a show of protest against Tokyo's plan to dispose of some 1.33 million metric tons of radioactive wastewater accumulated and stored in the destroyed Fukushima Daiichi Nuclear Power Plant.

On Tuesday, 11 lawmakers of the liberal opposition bloc -- nine from the main opposition Democratic Party of Korea and two independent lawmakers -- will issue a joint statement with a bipartisan anti-nuclear Japanese group of lawmakers advocating zero nuclear power and a renewable energy transition. The Korean group will also include three other opposition party members from the party's farmers and fishers committee, and four fishers.

This action will be part of their three-day visit to Japan that kicked off Monday morning, as the group labeled the latest report on the safety of Japan's "treated" wastewater from the International Atomic Energy Agency as "lacking scientific grounds."

"(The IAEA) never took other options than the wastewater discharge into the ocean into account, and there was no content related to the accumulation of radioactive materials in the human body nor about damage to the ecosystem at all in the report," Rep. Kim Seung-nam of the Democratic Party, a member of the group, said in a statement before the group departed from Seoul's Gimpo Airport.

"We will strengthen our solidarity with Japanese lawmakers, experts and civic groups to oppose the wastewater release plan and work to spread dissenting opinions in Korea about the plan. ... The wastewater release plan must be held off until the safety of the plan is guaranteed."

The Korean group on their first day of the trip held a protest in front of Japanese Prime Minister Fumio Kishida's office with Japanese activists.

Meanwhile, on Wednesday the group is poised to hold a press briefing for foreign correspondents based in Japan to explain its stance on the radioactive wastewater, then march through the streets to protest the discharge of the wastewater into the sea.

Another Democratic Party lawmaker, Rep. Jung Chung-rae, argued that Japan's burial of wastewater on its own soil would have been a more desirable option to dispose of the water, in a regular party meeting Monday. This remark came at the National Assembly against an image backdrop that included a statue of Adm. Yi Sun-sin, a historical figure who led naval victories to contain Japan in its invasions of Korea in the 1590s.

Veteran lawmaker of the Democratic Party Rep. Woo Won-shik was hospitalized Monday after holding a hunger strike for more than two weeks to protest the Japanese government's plan.

The opposition's moves show a sharp contrast from the government's stance on Japan's plan to release the wastewater treated through its Advanced Liquid Processing System to filter out most of the radioactive elements and dilute it with sea water, practically approved by the intergovernmental nuclear energy watchdog the previous week.

The ruling conservative People Power Party's Floor Leader Rep. Yun Jae-ok blasted the opposition on Monday for "undermining national interest while pursuing the party's own benefit," referring to the group's three-day visit to Japan and a tense meeting between IAEA chief Rafael Grossi and Democratic Party lawmakers.

Also on Monday, Park Ku-yeon, first vice minister of the Office for Government Policy Coordination, said in a daily briefing the use of the term "treated water" in line with the IAEA report to refer to the radioactive water of the Fukushima Daiichi Nuclear Power Plant is "far from being problematic."

Rather, Park said use of the term "nuclear wastewater" by the political opposition to refer to the water -- used to cool three of the plant's reactors after meltdowns due to the magnitude 9.0 earthquake and tsunami of 2011, and now stored in over 1,000 giant tanks at the plant -- is inappropriate, and that it "gives people groundless anxiety."

Park also played down rumors that the Japanese government had bribed Grossi.

Separately, Park again downplayed possibilities that Seoul would lift an import ban on Japanese seafood from eight prefectures, including Fukushima.

Seoul also braces for the water discharge plan's impact on the local consumption of domestic marine products due to fears about the water release plan.

Korea had earlier allocated a state budget of 175 billion won ($134.1 million) -- up more than twofold from 2022 -- to stockpile up to 76,000 tons of seafood and sea salt produced in Korea. It will also provide 115 billion won of financial aid to seafood and sea salt processing firms and dole out 64 billion won of vouchers to maintain consumer spending on Korean seafood and sea salt.