A recently discovered U.S. official document has confirmed that 12 American soldiers were killed in the 1945 atomic bombing of Hiroshima, making it the first known acknowledgment by the United States of how many of its captured military personnel died then.

A copy of the Dec. 20, 1948 report, titled "Death of 12 American fliers as a result of the atomic bombing on (Hiroshima)," had been written as part of an investigation into Japanese war crimes during World War II and whether the soldiers, who were Japan's prisoners of war, had been subject to abuses.

The one-page report, written by Capt. Robert Miller of the U.S. military, said that there was "insufficient evidence to prove an atrocity and no prosecutive action was taken," referring to trials for any such abuses, therefore concluding that the soldiers had died in the bombing of the western Japan city on Aug. 6, 1945.

Supplied photo shows some of the 12 U.S. soldiers, who were held as prisoners of war in Japan and were killed in the Aug. 6, 1945 atomic bombing of Hiroshima. (Courtesy of Shigeaki Mori)(Kyodo)

A copy of the report was obtained by Kyodo News from the U.S. National Archives, with the findings analyzed by Hitoshi Nagai, a professor of modern Japanese history at the Hiroshima Peace Institute.

Shigeaki Mori, an 86-year-old Japanese historian who is also a survivor of the bombing, was the first to mention the 12 victims in a book published in 2008, after conducting his own research and interviewing their bereaved family members.

During his 2016 visit to Hiroshima, then U.S. President Barack Obama mentioned the deaths of about "a dozen Americans held prisoners" in a speech, but the source for the figure was unknown.

The report did not mention the names of the 12 soldiers.

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