The BBC engaged in a "significant breach" of broadcasting rules by omitting to mention that the narrator of a programme about Gaza was the offspring of a Hamas official, according to regulatory body Ofcom.
An inquiry by Ofcom into Gaza: How to Survive a Warzone has found that the programme was "materially misleading".
The BBC's director general had already issued an apology, stating there had been "a significant failing in relation to truthfulness".
The authority has instructed the BBC to broadcast a peak-time declaration about its findings.
"Given this constitutes a major infringement of our regulations, we are instructing the broadcaster to transmit a message of our findings against it on BBC2 at 9pm, with a schedule to be determined," it said.
'Risk to Undermine Confidence'
The regulator's report said: "The inquiry we conducted determined that the film's failure to disclose that the narrator's male guardian occupied a post in the Hamas-run authority was materially misleading.
"This implied that the public did not have vital facts which may have been extremely pertinent to their assessment of the narrator and the content he shared.
"Credibility is at the center of the relationship between a media organization and its audience, notably for a state-funded media outlet such as the BBC.
"This error had the risk to damage the very considerable degrees of trust that audiences would have placed in a factual film from the broadcaster about the Gaza conflict."
The documentary was removed from the online platform in the month of February after the presenter's family links emerged, and in this past July an broadcaster's internal assessment found it violated the organization's content policies on factual correctness.
A BBC spokesperson commented: "The authority's determination is in line with the findings of Peter Johnston's review, that there was a significant failing in the documentary in relation to the BBC's Editorial Guidelines on accuracy, which aligns with Rule 2.2 of Ofcom's Broadcasting Code.
"We expressed regret for this and we agree with Ofcom's decision in complete. We will adhere to the sanction as soon as the date and language are confirmed."
