The BBC was found to have committed a "major breach" of industry standards by omitting to mention that the voice of a programme about Gaza was the son of a Hamas official, as determined by UK media regulator Ofcom.
An inquiry by Ofcom into Gaza: How to Survive a Warzone has concluded that the programme was "materially misleading".
The chief executive of the broadcaster had already issued an apology, stating there had been "a significant failing in relation to truthfulness".
Ofcom has directed the BBC to broadcast a prime-time declaration about its findings.
"As this represents a significant violation of our regulations, we are directing the broadcaster to air a announcement of our conclusions against it on the BBC's second channel at 21:00, with a timing to be finalised," it said.
'Risk to Erode Confidence'
The regulator's statement stated: "The inquiry we conducted found that the documentary's failure to disclose that the narrator's father held a post in the Hamas-run administration was materially misleading.
"It meant that the public did not have vital facts which may have been extremely pertinent to their assessment of the presenter and the content he shared.
"Trust is at the center of the connection between a media organization and its audience, notably for a public service broadcaster such as the public broadcaster.
"This error had the potential to damage the very considerable degrees of confidence that viewers would have put in a factual film from the broadcaster about the Gaza conflict."
The documentary was pulled from iPlayer in last February after the narrator's familial connections came to light, and in July an internal BBC review concluded it breached the broadcaster's editorial guidelines on factual correctness.
A corporation official commented: "The Ofcom ruling is in accordance with the findings of the internal assessment, that there was a serious error in the film in relation to the BBC's Editorial Guidelines on factual correctness, which reflects Rule 2.2 of the regulator's media standards.
"We expressed regret for this and we accept the authority's determination in complete. We will adhere to the penalty as soon as the date and language are confirmed."
