The phrase "unnamed official" refers to a person who provides information or gives a statement, but their name is not mentioned or disclosed. Full definition
And, on Friday, August 26, with Hurricane Irene approaching the city, the governor had an 11:50 a.m. call with unnamed officials at the MTA «re Status of Preparation of Subway Equipment, Facilities and Possible Evacuation Plan.» (politico.com)
The Houston Chronicle quotes unnamed officials as placing the blame for the problem squarely on humans. (aapaw.org)
The New York Times and CBS News, citing unnamed officials briefed on the matter, reported they included overseeing a hostile work environment as the White House doctor, allowed the overprescribing of drugs and drank on the job. (fortune.com)