ANKARA

A Japanese official said on Wednesday that the Fukushima nuclear water release is unrelated to the deaths of thousands of fish on Japan's northernmost main island of Hokkaido.

Mori Ken, an official with the Fisheries Agency of Japan, said authorities confirmed the presence of tritium in the ocean off the coast of Fukushima was below detectable levels.

"Insinuations that the fish die-off was caused by the treated water are unfounded," Japanese broadcaster NHK quoted Ken as saying.

He added that the spread of unverified information is a concerning situation.

Last week, hundreds of tons of dead sardines and mackerel fish washed up on a beach in northern Japan, creating a silver blanket that covered a 1.5-kilometer (less than a mile) stretch of shoreline around Toi fishing port in southern Hakodate on the northernmost main island of Hokkaido.

Officials estimated that at least 1,000 tons of mostly sardines but some mackerel washed ashore on Dec. 7, but warned that the figure could be higher.

Japan began releasing treated radioactive wastewater from the plant this August, triggering a strong reaction from China and opposition parties in South Korea and the Solomon Islands.

Beijing banned seafood imports from Japan after Tokyo went ahead with its plans. The plant has more than a million tons of treated wastewater to release throughout a 30-year process.

Following an earthquake and tsunami in 2011, the Fukushima plant was forced to shut down after facing the largest nuclear accident since 1986 in Chornobyl.

*Writing by Islamuddin Sajid