Declassified official U.S. documents showed Tuesday that the U.S. military estimated two days after its Aug. 6, 1945, atomic bombing of the city of Hiroshima that at least 100,000 people died as a result of the bombing.

The documents were released by the George Washington University's National Security Archive in Washington.

One of the documents, titled "Hiroshima Mission" and created by the U.S. Army Air Forces, said that the heart of the city of Hiroshima was so completely devastated by the atomic bombing that "not even debris of buildings was left," adding that it seemed as though the area had "never existed."

"The most conservative estimate here is that at least 100,000 of Hiroshima's inhabitants had been needlessly sacrificed by their military leaders," the document, dated Aug. 8, 1945, said.

The city of Hiroshima estimates that about 140,000 people died after the atomic bombing by the end of 1945.

Discussions within the then-U.S. government over atomic bomb demonstrations were also included in the newly released documents.

The National Security Archive said that while U.S. leaders have hailed the atomic bombings for bringing the war to an end, "many others have raised ethical questions about the use of weapons that caused so many civilian deaths and that in succeeding decades led to a costly and dangerous nuclear arms race."

The institute collects and studies official documents whose confidential designations have been lifted, based on the Freedom of Information Act. Since 2005, it has been advancing the disclosure of documents related to atomic bombs.