South Korea yesterday expanded its ban on Japanese seafood over fears of contamination from the Fukushima nuclear plant.
The government said it was responding to public fears as it accused Tokyo of not providing enough information on the crisis.
But the ban prompted a rebuke from Japan, which said Seoul should focus only on "scientific evidence".
Fisheries in Fukushima prefecture are closed, and fish caught in nearby prefectures are put on the market only after tests have shown them to be safe for consumption.
However, South Korea's ban now applies to a total of eight prefectures with a combined coastline of more than 700 kilometres, regardless of whether the fish pass safety standards or not. Consumption of fish products in South Korea has dropped sharply in recent weeks as Japanese workers struggle to contain leaks at the crippled facility.
Highly toxic water may have made its way into the Pacific Ocean, operator Tokyo Electric Power (Tepco) has admitted, and the utility also says up to 300 tonnes of mildly radioactive groundwater is making its way into the sea every day.
South Korea had previously put an import ban on dozens of fisheries products produced in Fukushima following the meltdown at the nuclear plant, triggered by the 2011 tsunami.
The government has now widened the ban to take in all such products from Fukushima and the seven other prefectures - Ibaraki, Gunma, Miyagi, Iwate, Tochigi, Chiba and Aomori.
The Ministry of Oceans and Fisheries said it had taken action as fears rose in South Korea.
"The measure comes as our people's concerns are growing over the fact that hundreds of tonnes of radiation-contaminated water leak every day from the site of Japan's nuclear accident in Fukushima," the ministry said in a statement.
"The government has concluded that the information provided by Japan so far has failed to make it clear how the incident will develop in the future. Under the new measure, all fisheries products from this region will be banned regardless of whether they are contaminated or not."
Chief Cabinet Secretary Yoshihide Suga challenged South Korea over the move.
"We are carrying out strict safe management on foods, including fishery products, based on international standards," he said.
"We would like the South Korean government to respond, based on scientific evidence."
Meanwhile, Hong Kong's Centre for Food Safety said it would continue to monitor the situation and had already banned fresh food imports from the five worst-hit prefectures.
"Due action will be taken if needed to ensure safety of food," the centre said.
Japan's fishermen yesterday rejected the proposed deliberate release of contaminated water into the ocean, a step the atomic regulator last week indicated may be needed.
A union of Japanese fisheries co-operatives said the discharge of any irradiated water would be unacceptable, even if contamination levels were brought below legal limits for ocean dumping.
The Japanese fishermen's group made its comments four days after Nuclear Regulation Authority chairman Shunichi Tanaka said the release of water, after being treated to remove most contaminants, could be a necessary part of managing growing volumes of irradiated water at the plant.
Tanaka's remark "is not something we fishermen can swallow by any measure," the association said.
Agence France Presse and Bloomberg. Additional reporting by Associated Press