Packages of frozen dried fish imported from Vietnam were found tainted with what is suspected to be pesticide and human feces, the Yamaguchi Prefectural Government said Thursday.

The substances were found inside cardboard boxes each containing 5 kg of the frozen fish in plastic bags at two supermarkets on July 15. It has not been confirmed whether the substances had direct contact with the fish, according to the prefecture.

A Yamaguchi-based importer has started a voluntary recall of the product, the prefecture said, adding that no health problems have been reported even though the product was shipped to Tokyo and nine other prefectures.

Subject to the recall are packages of frozen Icelandic capelin seasoned and packed in Vietnam by a company called Rich Beauty Food Co., according to the government. The volume of imports and the retailers involved are still under investigation.

The Health, Labor and Welfare Ministry said it ordered the distribution of the Vietnamese firm's products to be suspended in Japan and asked the Vietnamese government to investigate and take measures to prevent a recurrence.