The film, which parades an Oscar nominee, is set in Nigeria during a civil war. It is based on an award-winning novel, Half of a Yellow Sun, which the head of Nigeria's censorship board reportedly loved when it was premiered.

Yet, a week after the scheduled premiere in Nigeria, it still has not been shown in any theatre in Nigeria.

Many commentators on social media believe that the censors are afraid that tribal rivalries could be inflamed if the movie is shown in theatres across Africa's most populous nation.

Government censors are effectively banning the film but they will not say why, the film's director, Biyi Bandele, told the Associated Press (AP) yesterday.

He spoke in a phone interview from his home in London, where the movie placed among the 10 most popular cinemas over the Easter weekend. It debuts in the US on May 16.

The movie, which stars Oscar nominee Chiwetel Ejiofor ("12 Years a Slave" - the 2014 best picture Oscar) and Thandie Newton, is an adaptation of the book by Chimamanda Ngozi Adichie.

It is partly set during the 1967-1970 Nigerian civil war when the South-east sought to break away from the federation, and it comes at a time when Nigeria is threatened by an Islamic uprising in the North-east, threatening the unity between the mainly Muslim north and predominantly Christian south.

“More than 40 years after the end of the war, the problems that caused the war are even more pronounced," Bandele said. "I'm convinced that an organisation like Boko Haram (Islamic extremists) would not exist today if we had dealt with the root causes of the war.”

A ban on the movie would perpetuate the conspiracy of silence that has kept Nigerians from discussing the civil war, a subject that was pointedly excluded from history lessons in schools, Bandele said.

The National Film and Video Censors Board insisted it has not banned the movie but delayed its registration over “some unresolved issues which have to be sorted out”.

The movie's Nigeria premiere was set for last Friday, April 25. Invitations had been sent out and the film was to play in most theatres in the country. The previous day, the board told the distributors that the film had not yet passed the registration process.

About one million people died in the war for an independent Biafran nation for the Igbo people of the South-east, mainly Igbos who starved to death because food imports were blocked.

Then, leaders of the Igbo, who are almost exclusively Christians, accused the federal government of failing to protect them as Muslims from the Hausa tribe in the north slaughtered about 30,000 of them.

The tribal tensions and mistrust that led to that war remain strong. Today, some northern leaders accuse the federal government, led by a Christian southerner, of orchestrating mass killings of Muslims by soldiers in the North-east.

There are also conflicts over land and resources across the central part of the country that pit mainly Muslim Fulani herders against predominantly Christian farmers from other tribes.

Several members of the censorship board, including its director general Patricia Bala, viewed the film at its premiere at the Toronto Film Festival in September.

“She saw the movie and told us afterward how much she loved it and why (such) movies should be encouraged ... She was very encouraging, very positive and did not at any time express any reservations about the film,” Bandele said.

The board's website may offer a clue as to why it hasn't authorised the release of the film. The board's mission includes ensuring that “objectionable materials capable of inciting civil strife is reduced or eliminated completely” and banning materials that could “encourage racial, religious or ethnic discrimination or conflict”.

Bandele calls the film “a very, very faithful” adaptation of the novel, and says it is not a war flick. The book has been read by millions of Nigerians since its release in 2006, he said.

Many more millions of illiterate Nigerians would be able to appreciate it through the movie.

“This movie is a sort of love story, a love letter to Nigeria's very complex and complicated history, and it was meant to be a cautionary tale to say we can disagree as much as we want but war is never the answer,” he said.

There has still been no word on when the movie might be shown here, if it ever will.