WASHINGTON --- US Defense Secretary Lloyd Austin on Tuesday said the United States will investigate the recent purported leak of classified documents until the source of them was found. Reuters has reviewed more than 50 of the documents, labeled "Secret" and "Top Secret," that first appeared on social media sites in March and supposedly reveal details of the military capabilities of some U.S. allies and adversaries. Reuters has not independently verified the documents' authenticity. "We will continue to investigate and turn over every rock until we find the source of this and the extent of it," Austin said during a press conference at the State Department. Austin, the fir...Keep on reading: US will ‘turn over every rock’ to find source of leak – Pentagon chief