South Korean opposition lawmakers sharply criticized the head of the United Nations' nuclear watchdog on Sunday for its approval of Japanese plans to release treated wastewater from the damaged Fukushima nuclear power plant.

They met with Rafael Grossi in a tense meeting in Seoul that took place while protesters screamed outside the door.

Grossi, the International Atomic Energy Agency's (IAEA) director general, arrived in South Korea over the weekend to engage with government officials and critics and help reduce public concerns about food safety.

The IAEA last week approved the Japanese discharge plans, saying the process would meet international safety standards and pose negligible environmental and health impacts. South Korea's government has also endorsed the safety of the Japanese plans.

In his meeting with members of the liberal Democratic Party, which controls a majority in South Korea's parliament, Grossi said the IAEA's review of the Japanese plans was based on "transparent" and "scientific" research. He acknowledged concerns over how the Japanese plans would play out in reality and said the IAEA would establish a permanent office in Fukushima to closely monitor how the discharge process is implemented over the next three decades.

"Our conclusion has been that this plan, if it is carried out in the way it has been presented, would be in line, would be in conformity with the international safety standards," Grossi said.

The lawmakers responded by harshly criticizing the IAEA's review, which they say neglected the long-term environmental and health impacts of the wastewater release and threatens to set a bad precedent that may encourage other countries to dispose of nuclear waste into the sea. They called for Japan to scrap the discharge plans and work with neighboring countries to find safer ways to handle the wastewater, including a possible pursuit of long-term storage on land.

The party has also criticized the government of South Korean President Yoon Suk Yeol for putting people's health at risk while trying to improve relations with Japan.

"If you think (the treated wastewater) is safe, I wonder whether you would be willing to suggest the Japanese government use that water for drinking or for industrial and agricultural purposes, rather than dumping it in the sea," Woo Won-shik, a Democratic Party lawmaker who attended the meeting, told Grossi. The party said Woo has been on a hunger strike for the past 14 days to protest the Japanese discharge plans.

Further details from the meeting weren't immediately available after reporters were asked to leave following opening statements. Closely watched by parliamentary security staff, dozens of protesters shouted near the lobby of the National Assembly's main hall where the meeting was taking place, holding signs denouncing the IAEA and Japan.

Grossi was to fly to New Zealand later on Sunday and would then travel to the Cook Islands as he tries to reassure countries in the region about Japan's plans.

Hundreds of demonstrators had also marched in downtown Seoul on Saturday demanding that Japan scrap its plans.

(With input from AP)