The BBC engaged in a "major breach" of industry standards by failing to disclose that the presenter of a documentary about Gaza was the offspring of a Hamas representative, according to regulatory body Ofcom.
An investigation by the media regulator into Gaza: How to Survive a Warzone has concluded that the documentary was "substantially inaccurate".
The chief executive of the broadcaster had previously apologised, stating there had been "a major oversight in relation to accuracy".
The authority has directed the BBC to transmit a prime-time announcement about its decisions.
"As this represents a major infringement of our code, we are instructing the corporation to air a message of our conclusions against it on BBC2 at 9pm, with a schedule to be finalised," the statement read.
'Risk to Undermine Trust'
The authority's report declared: "Our probe concluded that the documentary's lack of disclosure that the voice's male guardian served in a position in the Hamas-administered authority was materially misleading.
"It meant that the public did not have essential details which may have been extremely pertinent to their judgment of the voice and the content he provided.
"Credibility is at the core of the bond between a broadcaster and its public, notably for a public service broadcaster such as the BBC.
"This oversight had the potential to erode the significantly high levels of trust that the public would have put in a factual film from the broadcaster about the Israel-Gaza war."
The programme was withdrawn from the BBC's streaming service in last February after the narrator's familial connections emerged, and in July an broadcaster's internal assessment concluded it violated the corporation's editorial guidelines on factual correctness.
A BBC spokesperson stated: "The regulator's decision is in line with the results of the corporation's inquiry, that there was a significant failing in the documentary in relation to the corporation's content standards on truthfulness, which reflects regulation 2.2 of Ofcom's Broadcasting Code.
"We issued an apology for this and we agree with the regulator's ruling in complete. We will comply with the sanction as soon as the timing and wording are confirmed."
