"'The Silent Majority Speaks', the admirable visual essay of filmmaker Bani Khoshnoudi, has been censored in Beirut," a statement from the Cultural Resistance International Film Festival organisers said.
"The film was to be screened tonight... At noon, the Censorship Committee served notice to the festival's organisers that it was banned for 'insulting a foreign country,'" the statement added.
"The organisers of the festival protest this ban, which risks depicting Lebanon as a backwards and unenlightened country in the eyes of the international community."
Lebanon's Censorship Committee is part of the General Security agency and monitors all films before screening in the country.
General Security is regarded as close to Lebanon's powerful Hezbollah movement, which is allied with Iran.
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The film, a documentary, includes scenes depicting the protests that erupted in Iran after the 2009 presidential elections that returned Mahmoud Ahmadinejad to power despite claims of election fraud.
Festival director Jocelyne Saab described the censorship decision as "dangerous".
"There is nothing in the film that justifies the ban," she told AFP.
"It narrates what happened in a beautiful artistic way and is not intended to criticise or attack but to create dialogue," she added.
Lebanon is considered one of the most open societies in the Middle East, but art is occasionally censored, usually for sexual content or sensitive religious issues, rather than for political reasons.
The Cultural Resistance Film Festival is in its second year and is screening movies in five locations in Lebanon.
Saab said the works selected were "to be a mirror for us, to teach us lessons and encourage dialogue."