The BBC engaged in a "significant breach" of media regulations by omitting to mention that the narrator of a film about Gaza was the son of a Hamas official, according to UK media regulator Ofcom.
An probe by the broadcasting watchdog into the programme Gaza: How to Survive a Warzone has found that the film was "materially misleading".
The BBC's director general had previously apologised, noting there had been "a significant failing in relation to factual correctness".
Ofcom has ordered the BBC to air a peak-time declaration about its findings.
"Since this amounts to a serious breach of our regulations, we are instructing the broadcaster to transmit a message of our conclusions against it on BBC Two at nine o'clock in the evening, with a timing to be finalised," it said.
'Possibility to Undermine Confidence'
The regulator's report stated: "Our probe found that the film's omission to reveal that the narrator's male guardian served in a role in the Hamas-controlled administration was substantially inaccurate.
"This implied that the public did not have essential details which may have been very significant to their assessment of the voice and the information he presented.
"Trust is at the core of the relationship between a media organization and its public, particularly for a public service broadcaster such as the British Broadcasting Corporation.
"This failing had the potential to damage the exceptionally strong degrees of credibility that viewers would have placed in a BBC factual programme about the conflict in Gaza."
The programme was pulled from the BBC's streaming service in last February after the narrator's familial connections came to light, and in this past July an internal BBC review found it infringed the corporation's journalistic standards on accuracy.
A corporation official said: "The regulator's decision is in line with the findings of Peter Johnston's review, that there was a major oversight in the documentary in relation to the corporation's content standards on factual correctness, which reflects clause 2.2 of the authority's broadcasting regulations.
"We have apologised for this and we comply with the authority's determination in complete. We will adhere to the penalty as soon as the timing and language are determined."
