The National Archives and Records Administration discovered what it believed was classified information in documents Donald J. Trump had taken with him from the White House as he left office, according to a person briefed on the matter.

The discovery, which occurred after Mr. Trump returned 15 boxes of documents to the government last month, prompted the National Archives to reach out to the Justice Department for guidance, the person said. The department told the National Archives to have its inspector general examine the matter, the person said…

After the F.B.I., during the 2016 presidential campaign, investigated Hillary Clinton’s handling of classified material while she was secretary of state, Mr. Trump assailed her, helping make the issue pivotal in the outcome of that race. In that case, the intelligence community’s inspector general had made a national security referral to the F.B.I., prompting the investigation of Mrs. Clinton.