The BBC engaged in a "significant breach" of broadcasting rules by not revealing that the presenter of a film about Gaza was the offspring of a Hamas official, as ruled by regulatory body Ofcom.
An inquiry by Ofcom into Gaza: How to Survive a Warzone has determined that the programme was "materially misleading".
The head of the BBC had already issued an apology, saying there had been "a significant failing in relation to accuracy".
The authority has instructed the corporation to transmit a evening declaration about its decisions.
"As this represents a major infringement of our rules, we are instructing the BBC to air a statement of our determinations against it on the BBC's second channel at 21:00, with a schedule to be finalised," the regulator stated.
'Risk to Damage Trust'
The authority's statement stated: "The inquiry we conducted determined that the programme's omission to reveal that the voice's male guardian held a post in the Hamas-run government was significantly deceptive.
"It meant that the public did not have essential details which may have been extremely pertinent to their assessment of the voice and the content he provided.
"Credibility is at the heart of the bond between a television network and its audience, particularly for a national broadcasting corporation such as the public broadcaster.
"This error had the possibility to damage the significantly high degrees of trust that the public would have placed in a documentary produced by the BBC about the conflict in Gaza."
The documentary was removed from the BBC's streaming service in February after the narrator's family links emerged, and in this past July an broadcaster's internal assessment determined it infringed the corporation's content policies on truthfulness.
A BBC spokesperson said: "The regulator's decision is in line with the findings of the internal assessment, that there was a serious error in the documentary in relation to the corporation's content standards on truthfulness, which reflects clause 2.2 of the authority's broadcasting regulations.
"We expressed regret for this and we comply with Ofcom's decision in its entirety. We will comply with the sanction as soon as the timing and language are finalised."
