SHANGHAI (Kyodo) Two Japanese nationals in their 50s received heart transplants between 2001 and 2004 at a Shanghai hospital whose organs mainly come from death-row inmates, sources at a Taiwanese company that arranged the procedures said Thursday.

Japan was seemingly unaware of the cases, as a survey released March 9 by the Health, Labor and Welfare Ministry said there were no cases of Japanese receiving heart transplants in Asia outside of Japan.

Ethical and medical concerns have often been raised regarding organ transplants in China over issues that include the use of organs of prisoners on death row and uncertain postsurgery health-care, experts said.