The main opposition Democratic Party(DP) has ramped up its offensive against the government ahead of Friday’s return of a team of experts sent to inspect Japan's plans to release radioactive water from the crippled Fukushima nuclear plant into the ocean.

At a Supreme Council meeting, DP leader Lee Jae-myung said the expert team does not appear to have the will to probe Tokyo's preparations but merely act as lackeys to shield the Japanese government's position.

Referring to Tokyo's request for Seoul to resume imports of seafood from Fukushima, Lee urged President Yoon Suk Yeol to issue an edict that imports will not resume from the region under any circumstance.

Supreme Council member Ko Min-jung called for a case to be brought to the International Tribunal for the Law of the Sea as well as a tentative measure to stop Tokyo from releasing the water before a decision by the tribunal.

The DP chief and the rest of party leadership attended a kickoff ceremony in Seoul's Gwanghwamun on Friday morning for a nationwide campaign to obtain signatures opposing the water release and import resumption.

The party plans to put forth a resolution opposing the water release and calling for a special parliamentary inspection committee, while also seeking to hold a hearing with testimonies from the experts on the inspection team.