Japan's Foreign Ministry says additional monitoring has been carried out on treated and diluted water discharged into the ocean from the damaged Fukushima Daiichi nuclear plant.

The extra tests are a prerequisite for China to resume imports of Japanese seafood.

Water used to cool molten fuel at the plant has been mixing with rain and groundwater. The accumulated water is treated to remove most radioactive substances, but still contains tritium.

Before releasing the treated water into the ocean, the plant's operator dilutes it to reduce tritium levels to about one-seventh of the World Health Organization's guidance level for drinking water.

Japan and China agreed last month that China would resume imports of Japanese seafood that meet safety standards after additional monitoring of the discharged water within the framework of the International Atomic Energy Agency. The two countries had been adjusting the timing of the tests.

Foreign Ministry Press Secretary Kitamura Toshihiro said on Wednesday that the planned additional procedures, including sampling of seawater by institutions in China and two other countries, were conducted on Tuesday.

Kitamura said Japanese Prime Minister Ishiba Shigeru lobbied Chinese Premier Li Qiang on the issue at their summit last week in Laos.

He added that Japan will continue to urge China to resume imports as soon as possible.