Which american leader while attending the potsdam conference issued a warning to japan to surrender or face complete destruction

President Harry Truman.

The Potsdam Declaration was issued in July, 1945, by President Truman along with Great Britain's prime minister,Winston Churchill, and China's leader, Chiang Kai-shek. The statement declared that the full military power of the Allies was prepared "to prosecute the war against Japan until she ceases to resist," and that "the full application of our military power, backed by our resolve, will mean the inevitable and complete destruction of the Japanese armed forces and just as inevitably the utter devastation of the Japanese homeland."  They said the time had come for Japan to decide whether to continue to follow the "unintelligent calculations" of their nation's "militaristic advisers," or whether the Japanese people would "follow the path of reason."