Prior to the atomic attacks on Hiroshima and Nagasaki, elements existed within the Japanese government that were trying to find a way to end the war. In June and July 1945, Japan attempted to enlist the help of the Soviet Union to serve as an intermediary in negotiations. No direct communication occurred with the United States about peace talks, but American leaders knew of these maneuvers because the United States for a long time had been intercepting and decoding many internal Japanese diplomatic communications. From these intercepts, the United States learned that some within the Japanese government advocated outright surrender. A few diplomats overseas cabled home to urge just that.
https://www.osti.gov/opennet/manhattan-project-history/Events/1945/surrender.htm