South Korea has banned all fisheries imports from eight Japanese prefectures, amid concern over leaks of radioactive water from the crippled Fukushima nuclear plant.
A spokesman said the measure was due to "sharply increased" public concern about the flow of contaminated water into the sea.
The ban, an expansion of existing restrictions, takes effect on Monday.
The Fukushima plant has been hit by a series of water leaks in recent months.
The earthquake and tsunami in March 2011 knocked out cooling systems to reactors, three of which melted down.
Water is now being pumped in to cool them, but storing the resultant large quantities of radioactive water has proved a challenge for plant operator Tokyo Electric Power Company (Tepco).
The contaminated water is being stored in temporary tanks, but leaks from the tanks, pipes and through damaged structures have been a persistent problem.
Groundwater from the hills surrounding the plant also flows down and into the radioactive areas.
"The measures are due to the sharp increase in concern from the public about the flow of hundreds of tonnes of contaminated water into the ocean at the site of the Fukushima nuclear accident in Japan," spokesman for the South Korean prime minister's office Shin Joong-don said.
The government felt it was "unclear" how the incident would develop and that information provided by the Japanese government was "not enough to predict future developments".
South Korea already had a ban on 50 fisheries products from Fukushima and seven surrounding prefectures in place.
Japan, however, said fisheries exports were safe for consumption.
"We are conducting strict safety controls based on international standards. If (radiation) readings are above the standards, shipment will be stopped," top government spokesman Yoshihide Suga said.
Earlier this week, the Japanese government pledged 47bn yen ($473m, £304m) in funding for measures to tackle the leak problem, including the construction of an earth "ice wall" around the reactors and an upgraded water treatment system.