The BBC engaged in a "major breach" of media regulations by not revealing that the presenter of a programme about Gaza was the child of a Hamas representative, as ruled by UK media regulator Ofcom.
An inquiry by Ofcom into the programme Gaza: How to Survive a Warzone has found that the film was "substantially inaccurate".
The chief executive of the broadcaster had already issued an apology, saying there had been "a significant failing in relation to accuracy".
The authority has directed the corporation to transmit a peak-time declaration about its findings.
"As this represents a major infringement of our code, we are ordering the BBC to broadcast a message of our conclusions against it on the BBC's second channel at nine o'clock in the evening, with a date to be confirmed," the regulator stated.
The watchdog's report declared: "The inquiry we conducted found that the documentary's omission to reveal that the presenter's male guardian held a role in the Hamas-run government was substantially inaccurate.
"This implied that the viewers did not have vital facts which may have been extremely pertinent to their judgment of the voice and the content he shared.
"Confidence is at the center of the connection between a media organization and its audience, especially for a state-funded media outlet such as the British Broadcasting Corporation.
"This error had the possibility to erode the exceptionally strong degrees of trust that viewers would have put in a documentary produced by the BBC about the conflict in Gaza."
The programme was pulled from iPlayer in February after the narrator's family links were revealed, and in the month of July an internal BBC review found it violated the corporation's journalistic standards on factual correctness.
A corporation official stated: "The authority's determination is in accordance with the results of the internal assessment, that there was a major oversight in the film in relation to the BBC's Editorial Guidelines on factual correctness, which corresponds to Rule 2.2 of the authority's broadcasting regulations.
"We issued an apology for this and we agree with the regulator's ruling in its entirety. We will adhere to the penalty as soon as the schedule and wording are finalised."
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