Facebook owner Meta should not have taken down posts featuring a slogan calling for the death of Iranian supreme leader Ayatollah Khameini, a watchdog said on Monday.
Facebook moderators decided last July that posts featuring the Persian slogan "marg bar Khameini," literally translated as "death to Khameini," broke the firm's guidelines against inciting harm or killing.
But the Facebook Oversight Board, an independent panel funded by Meta whose decisions are binding on the company, ruled that the slogan was not a credible threat and broke no guidelines.
The board accepted that the literal translation was "death to..." but in the context of Iranian protests its meaning was closer to "down with...."
The offending post came months before the nation was convulsed by protests over the brutal treatment of women at the hands of the religious authorities.
The initial spark was the death in September of 22-year-old Mahsa Amini after the morality police had taken her into custody over claims she had breached the rules on Muslim headwear.
The Oversight Board said the earlier decision to take down posts with the "death to..." slogan had affected the role of Meta's platforms, which include Instagram, in the protests.
"In the Iranian context, the Board finds that Meta must do more to respect freedom of expression, and permit the use of rhetorical threats," it said.
"As this case shows, its failure to do so led to the silencing of political speech aimed at protecting women's rights."
The board called for the company to clarify its rules to allow criticism of heads of state, particularly including rhetorical threats made during protests.
Last year's demonstrations were the biggest the Islamic republic has seen in years.
Iran's rulers have now meted out death sentences to 17 people over alleged crimes committed during the protests, sparking global outrage and new Western sanctions.