A National Security Agency internal review of damage caused by the former contractor Edward Snowden has focused on a particular area of concern: the possibility that he gained access to sensitive files that outline espionage operations against Chinese leaders and other critical targets, according to people familiar with aspects of the assessment.

The possibility that intelligence about foreign targets might be made public has stirred anxiety about the potential to compromise the agency’s overseas collection efforts. U.S. officials fear that further revelations could disclose specific intelligence-gathering methods or enable foreign governments to deduce their own vulnerabilities.

“We’re deeply concerned,” said one senior intelligence official, who, like others interviewed for this article, was not authorized to speak on the record. “The more that this gets made public, the more capability we lose.”…

“He got a lot,” the official continued, but it was “not even close to the lion’s share” of what the NSA is engaged in. Still, the official said, harm to the efforts “is a concern.”