A total of 174 foreigners working as part of Japan's technical intern program died over the eight years until 2017 due to accidents, illness and other reasons, according to a government tally released Tuesday.

The revelation raises questions about the working conditions of foreign trainees at a time when Japan is preparing to accept more overseas workers from April to address the country's labor crunch.

Opposition parties have been urging the government to investigate technical interns' deaths, pointing to the possibility they were subjected to harsh working conditions. They are demanding the government improve such situations before many of the workers switch their statuses under the new visa system to be introduced.

The deaths included suicides and cases in which causes of death were not clear, sources familiar with the matter said, adding 132 were men and 42 women.

People in their 20s accounted for the largest portion with 118, followed by 48 in their 30s. Five were teens and three were in their 40s.

Many of the deaths resulted from accidents that happened while workers were operating factory machines such as metal cutters or timber processing equipment. Among the non-accidental reasons, health problems such as a heart attack and stroke stood out. There were 13 suicides.

Two technical interns died in the March 2011 tsunami triggered by a devastating earthquake in Japan's northeast.

The data comes a week after an opposition lawmaker disclosed the deaths of 69 foreign trainees between 2015 and 2017 based on a Justice Ministry tally. The ministry has said it will look into the matter.

Japan introduced the training program for foreigners in 1993 with the aim of transferring skills to developing countries. But the scheme has been criticized for providing cover for companies to import cheap labor.

As of the end of October last year, about 258,000 foreign trainees were working in Japan.