The BBC committed a "serious breach" of industry standards by not revealing that the presenter of a programme about the Gaza conflict was the offspring of a Hamas representative, according to regulatory body Ofcom.
An probe by the media regulator into Gaza: How to Survive a Warzone has determined that the documentary was "substantially inaccurate".
The chief executive of the broadcaster had previously apologised, saying there had been "a significant failing in relation to factual correctness".
The regulator has ordered the broadcaster to transmit a evening declaration about its decisions.
"Since this amounts to a major infringement of our code, we are instructing the BBC to transmit a statement of our findings against it on BBC2 at nine o'clock in the evening, with a timing to be finalised," it said.
'Possibility to Erode Confidence'
The authority's report declared: "Our investigation found that the programme's omission to reveal that the narrator's male guardian occupied a position in the Hamas-administered authority was substantially inaccurate.
"This implied that the viewers did not have essential details which may have been extremely pertinent to their judgment of the narrator and the details he presented.
"Confidence is at the core of the bond between a media organization and its viewers, particularly for a state-funded media outlet such as the public broadcaster.
"This error had the potential to undermine the exceptionally strong degrees of trust that viewers would have placed in a factual film from the broadcaster about the conflict in Gaza."
The programme was withdrawn from the BBC's streaming service in February after the presenter's personal associations came to light, and in this past July an internal BBC review concluded it violated the organization's journalistic standards on accuracy.
A corporation official said: "The authority's determination is in accordance with the findings of Peter Johnston's review, that there was a major oversight in the film in relation to the BBC's Editorial Guidelines on factual correctness, which aligns with clause 2.2 of Ofcom's Broadcasting Code.
"We have apologised for this and we comply with the regulator's ruling in full. We will follow the sanction as soon as the schedule and wording are confirmed."