Snowden, U.S. officials said, took tens of thousands of documents, some of which contain sensitive material about collection programs against adversaries such as Iran, Russia and China. Some refer to operations that in some cases involve countries not publicly allied with the United States…

In one case, for instance, the files contain information about a program run from a NATO country against Russia that provides valuable intelligence for the U.S. Air Force and Navy, said one U.S. official, who requested anonymity to discuss an ongoing criminal investigation. Snowden faces theft and espionage charges.

“If the Russians knew about it, it wouldn’t be hard for them to take appropriate measures to put a stop to it,” the official said.

Snowden lifted the documents from a top-secret network run by the Defense Intelligence Agency and used by intelligence arms of the Army, Air Force, Navy and Marines, according to sources, who spoke on the condition of anonymity to discuss sensitive matters.