South Korea will tighten its regulations on food imports from Japan amid worries of radioactive contamination.

The Korea Food and Drug Administration (KFDA) said that it would demand a food safety certificate from Japan as of May when importing foods produced in 13 Japanese regions, including Tokyo, Kanazawa, Shizuoka, and Nagano. Radioactive substances have been detected in food products from those locations.

The 13 regions will need certification on agricultural products and processed foods.

A KFDA official predicts that food imports from Japan will be halted in effect as there is a limit to the Japanese government’s ability to test its foods for safety and that the administration will demand additional tests when radiation is detected.

The KFDA also lowered the permissible levels of radioactive iodine in food items for infants to less than 100 becquerels per kilogram.