But since then the department confirmed that Mr. Holder had approved a request for a search warrant in 2010 for the private correspondence of James Rosen, a Fox News reporter who disclosed a North Korean nuclear test that had not been made public.

An affidavit filed in the investigation seeking Mr. Rosen’s e-mails said there was probable cause to believe Mr. Rosen had violated the Espionage Act, arguing that he qualified for an exception to a law that generally bars search warrants for reporters’ work unless the reporter is suspected of committing a crime.

The Justice Department letter, signed by Peter J. Kadzik, principal deputy assistant attorney general, noted that while a grand jury did charge a government employee with the unauthorized disclosure of classified information, Mr. Rosen has not been charged with anything. “At no time during the pendency of this matter — before or after seeking the search warrant — have prosecutors sought approval to bring criminal charges against the reporter,” Mr. Kadzik wrote.