The excised portion of the Dec. 2, 2013, briefing included a question about whether an earlier spokeswoman for the department had misled reporters about whether the United States was holding secret direct nuclear talks with Iran.

The State Department initially said it believed a "glitch" caused the gap but on Wednesday said an internal inquiry found it was a deliberate omission. However, it said no rules were broken because none existed governing the integrity of the briefing transcript and video. Rules are now being put in place.

The inquiry was carried out by the department's Office of the Legal Adviser at the request of State Department spokesman John Kirby, who is also assistant secretary of the department's Bureau of Public Affairs.

"In so doing, they learned that a specific request was made to excise that portion of the briefing. We do not know who made the request to edit the video or why it was made," Kirby told reporters at his daily briefing.

The video editor who received the request by telephone "does not remember anything other than that the caller was passing on a request from someone else in the (Public Affairs) bureau," Kirby added.

Speaking on condition of anonymity, a U.S. State Department official said the editor discussed the request with her supervisor and concluded that it came from a "level of credibility and authority" high enough that they should act on the request.

Kirby said the video had been replaced some time ago with a full version that was archived with the Defense Department. He said the transcript of the briefing had always been available online and had not been modified.

(Reporting by Arshad Mohammed and David Alexander; Editing by Eric Walsh and James Dalgleish)