Japan's welfare ministry has said the remains of 597 people collected from burial sites in Siberia in Russia's Far East may not be of Japanese postwar internees.
The ministry announced the results of its probe on Thursday. It comes after NHK reported that the ministry failed to address suspicions over the possible mix-up of remains for at least 14 years.
An estimated 55,000 Japanese died of hard labor in the bitter cold while interned by the former Soviet Union just after World War Two.
Ministry officials say they examined the remains collected from 126 burial sites in Siberia and elsewhere since 1999. It showed that those of 597 people from nine sites in Khabarovsk, Irkutsk and other regions may not be of Japanese.
DNA experts who examined the remains had repeatedly told the ministry since 2005 that some of the remains collected in Siberia were unlikely to be of Japanese.
But the ministry did not make the suspicions public and did not address the issue.
Ministry officials say it took time to study the issue internally and they were not able to discuss it with the Russian side yet.
They say they do not think they just left the issue unaddressed, but will accept the criticism that they lacked speed in taking action.
Ministry officials say they will carry out further DNA tests on those remains to determine whether they were of Japanese or not. They also say they will look into what went wrong with their collection project.