Highly classified Pentagon documents leaked online in recent weeks have provided a rare window into how the U.S. spies on allies and foes alike, deeply rattling U.S. officials, who fear the revelations could jeopardize sensitive sources and compromise important foreign relationships.
The information was reportedly based in part on intercepted communication signals.
Some of the documents, which U.S. officials say are authentic, expose the extent of U.S. eavesdropping on key allies, including South Korea, Israel and Ukraine.