It is a coming-of-age tale of two girls, the daughters of political opponents, who fall in love and find their identity and dreams compromised by a conservative society.

Bringing their story to the screen has proved a triumph for director Wanuri Kahiu, who made history last week after it was announced that Rafiki would be the first Kenyan film to feature at the Cannes film festival, which begins in May.

Yet the fiction is all too close to reality after it was announced on Friday that Kenyan authorities have banned the film due to its “clear intent to promote lesbianism”.

According to the Kenya Film Classification Board (KFCB), the movie Rafiki – which means “friend” in KiSwahili – contravenes national laws and culture.

Ezekiel Mutua, the board’s chief executive, announced: “The Kenya Film Classification Board has banned the film Rafiki due to its homosexual theme and clear intent to promote lesbianism in Kenya contrary to the law and dominant values of the Kenyans.”

Oddly, the ban comes just days after Mutua applauded the award-winning director Kahiu, who won a clutch of accolades for her 2008 film, From a Whisper.

Speaking in a live radio interview he said: “I had a great meeting with Wanuri Kahiu, one of the greatest Kenyans that we have in the film industry and her movie has been nominated. Cannes is big. Other than the Oscars, Cannes is the best.”

Yet a press statement issued on Friday warned that anyone who distributed, exhibited or broadcast the film in Kenya, or was found to be in possession of the film, would be in breach of the law.

Kahiu took to Twitter to express her dismay, writing: “I am incredibly sorry to announce that our film Rafiki has been banned in Kenya. We believe adult Kenyans are mature and discerning enough to watch local content but their right has been denied.”

Homosexuality is illegal in Kenya and gay sex is punishable by 14 years in prison.

The statement said the decision to ban the film had been taken with “various stakeholders and agencies of law”.

It went on to allege that the producers of the film broke the law by altering the film script they originally submitted for licensing without permission.

Rafiki, inspired by the 2007 Caine prize-winning short story Jambula Tree by Ugandan writer Monica Arac de Nyeko, follows Kena (Samantha Mugatsia) and Ziki (Sheila Munyiva), who fall in love despite the odds stacked against them.

The KFCB claims romantic scenes depicting the lead actors as lesbians were absent in the original script and that it would pursue legal avenues to holding the producers to account.

“In the script the lead actors were portrayed as having been attacked for political reasons, having formed a political party feigning unity between their parents whereas in the film they were obviously attacked for being homosexual,” it said in a statement.

It also signalled a warning to foreign agencies involved in the promotion of the film, urging them to respect Kenyan culture and “desist from funding content that undermines the sensibilities of the Kenyan people”.

It said: “Hare-brained schemes by foreigners funding film producers in Kenya to promote homosexuality in the name of equality and inclusion will be exposed and strongly resisted.”

Board spokeswoman Nelly Muluka tweeted: “Our culture and laws recognise family as the basic unit of society. The [board] cannot, therefore, allow lesbian content to be accessed by children in Kenya.”

Kahiu said: “I’m really disappointed because Kenyans already have access to watch films that have LGBT content, on Netflix, and in international films shown in Kenya and permitted by the classification board itself.

“So to then just ban a Kenyan film because it deals with something already happening in society just seems like a contradiction.”

Homosexuality is taboo across the majority of African nations and people who are gay face discrimination or persecution. In recent years, however, campaigners for lesbian, bisexual, gay and transgender rights have become increasingly vocal.

The ban coincides with a landmark case brought by gay rights campaigners to repeal Kenya’s law on gay sex on the grounds that it deprives sexual minorities of basic rights.

The film commission used a hashtag, #KFCBbansLesbianFilm, that immediately sparked a barrage of supportive tweets from Kenyans who decried homosexuality.