Kyodo News In the report, researchers at the University of Auckland determined that the meat, sold in August and October as minke whale at shops in Taiji and Nachikatsuura, both in Wakayama Prefecture, was in reality gray whale.
The researchers will demand that the Fisheries Agency and its affiliate, the Institute of Cetacean Research, identify where the meat came from.
The government, however, denied the report, saying genetic analyses done by the researchers are questionable.
The hunting of gray whales is banned under a 1937 international whaling agreement.
Japan is allowed to sell gray whale meat only in an area where a whale has beached itself or was caught in a set net. However, the researchers said no gray whale has been captured near Wakayama.
A whaling expert said the meat is probably from a gray whale that was found dead floating in the Sea of Japan near Suttsu in Hokkaido, about 1,000 km northeast of Wakayama, in May 1996.
An official of the Fisheries Agency's Far Seas Fisheries Division flatly denied the report, and said the researchers are refusing to provide a sample of the meat for verification.