Truman had mentioned an unspecified "powerful new weapon" to Stalin during the conference. Towards the end of the conference, on July 26, the Potsdam Declaration gave Japan an ultimatum to surrender unconditionally or meet "prompt and utter destruction", which did not mention the new bomb but promised that "it was not intended to enslave Japan". The Soviet Union was not involved in that declaration since it was still neutral in the war against Japan. Japanese Prime Minister Kantarō Suzuki did not respond, which was interpreted as a sign that the Empire of Japan had ignored the ultimatum. As a result, the United States dropped atomic bombs on Hiroshima on 6 August 1945 and Nagasaki on 9 August. The justifications used were that both cities were legitimate military targets and that it was necessary to end the war swiftly and preserve American lives.