A former doctor in Japan's World War II navy says he was ordered to perform medical experiments on Filipino prisoners before they were executed.
Few veterans of Japan's imperial forces have spoken of atrocities
Akira Makino, 84, told Kyodo news agency he performed surgery and amputations on condemned prisoners, including women and children.
Japan's imperial forces are believed to have carried out medical experiments on prisoners captured in China.
Few Japanese veterans have spoken of atrocities committed during the war.
The BBC's Chris Hogg says most want to put the past behind them and they have had little encouragement from the authorities to offer an account of what happened.
Mr Makino's testimony is believed to be the first account from a Japanese veteran of the war in south-east Asia describing medical experiments on prisoners.
Mr Makino was stationed on the island of Mindanao in the Philippines during World War II.
He told the Kyodo news agency he had operated on some 30 prisoners between December 1944 and February 1945.
The operations - which included amputations and abdominal surgery - were regarded as part of his medical training, he said.
"I would have been killed if I had disobeyed the order," Mr Makino said. "That was the case in those days."
He also said he was disgusted by orders to practise surgery on two Filipino men, rendered unconscious after being captured on suspicion of being US spies.
"I thought, 'What a horrible thing I'm doing to innocent people even though I'm ordered to do it'," he said.
Mr Makino said he was still haunted by the memories of his work in the Philippines.
"We should not repeat such miseries again," he said. "I want to tell the truth about the war, even if it is to only one person or two."
A Japanese army unit specialising in biological warfare is believed to have carried out medical tests on prisoners during the wartime occupation of north-eastern China.
At least 3,000 prisoners are believed to have died at the hands of the unit.
Japan has acknowledged the unit's existence but has not charged anyone in connection with allegations of atrocities.