South Korea is to ban all fish imports from eight Japanese prefectures, because of radiation contamination from the crippled Fukushima nuclear power-plant.
South Korea has already banned 50 fishery products from the prefectures and will now tighten its testing on fishery imports from other areas of Japan.
A spokesperson for the Prime Minister's office said on Friday the measures were in response to sharply increased public concern about contaminated water in the ocean at the site of the nuclear disaster in March 2011.
After months of denials, the Tokyo Electric Power Company admitted in July that contaminated groundwater was leaking into the sea.
The ban takes effect on Monday and will remain in place indefinitely. Some of Japan's biggest fishing areas are affected.
Vice Fisheries Minister Son Jae-hak said information received from Japan was not good enough to properly judge the situation.
South Korea imported 5000 tonnes of fishery products from the eight affected prefectures last year, out of a total of 40,000 tonnes of imports from Japan.
TEPCO said last month that 300 tonnes of toxic water leaked from a tank storing contaminated run-off. It has since found radiation hotspots in three other holding areas.
The government this week pledged nearly $US500 million to help TEPCO try to contain the contaminated water.
China has also banned imports of dairy, vegetable and seafood products from at least five Japanese prefectures since the disaster
