The release of the Nigerian civil war film "Half of a Yellow Sun", which had been set to open in cinemas nationwide on Friday, has been delayed by the country's censorship board. The film based on the eponymous best-selling novel by Chimamanda Ngozi Adichie is about the 1967-1970 Biafra War which killed more than a million people, many from starvation. A statement on the film's website said the Nigeria release has been "postponed to May 2 due to delays in getting certification from the Nigeria Film and Video Censorship Board". Board spokesman Caesar Kagho told AFP there were "regulatory issues" with the release, but that the film had not been "officially banned". The firm handling distribution in Nigeria, Filmhouse Cinemas, met with censors on Friday in a bid to resolve the dispute, the company's chief Kene Mkparu told AFP. He said the delay was linked to the film's content but declined to be more specific, adding that the company would provide further details later. "Half of Yellow Sun" stars Chiwetel Ejiofor, nominated for Best Actor at the Academy Awards for his role in "12 Years a Slave," named 2014's Best Picture. - Controversial topic - The Biafra War began after the eastern region tried to secede from the newly independent Nigeria. The East, dominated by members of the Igbo ethnic group, claimed their tribesman were being massacred in the mainly Muslim north and accused the federal government of failing to provide protection. Their attempt to create an independent Igbo-led nation, which they called Biafra, was crushed by British-backed federal forces which had military superiority and used scorched earth tactics, including the blockage of all food imports to the breakaway region. More than four decades on, the Biafra War remains a highly contentious subject in Nigeria. In his last published work before his death in 2013, acclaimed Nigerian author Chinua Achebe, an Igbo, sparked a heated debate about the conflict that raged on television and in newspapers for weeks. In "There Was A Country," Achebe accused a revered leader from the Yoruba-dominated West, Obafemi Awolowo, of supporting the starvation of Igbos to further his own political goals. Yoruba leaders reacted furiously to the charge and the debate further highlighted the lingering bitterness from the conflict. - Highly anticipated - "Half of a Yellow Sun", which had its global premiere at last year's Toronto International Film Festival, is already showing in Britain and Australia and is scheduled to open soon in the United States and other countries. Anticipation about the release had been building in Nigeria's largest city and cultural hub Lagos, notably after cast members, including Ejiofor, visited the city for the premiere earlier this month. Ejiofor's parents are from eastern Nigeria and much of his family was affected by the Biafra War. There were ads in several Nigerian dailies on Friday promoting the film which was shot entirely in the southeastern state of Cross Rivers. The censorship board, which is not widely known to ban films, has objected to some recent controversial work. Censors last year resisted the Nigerian release of a Ghanaian-made movie about the Islamist insurgent group Boko Haram called "Nation Under Siege," and most cinema owners refused to screen it, according to the producers. While details surrounding the "Half of Yellow Sun" postponement were not yet clear, some on social media have accused the censors of trying to suppress a story about one of Nigeria's most defining episodes. "We say the West doesn't tell our stories, we say we want investment in our film industry, yet when 'Half of Yellow Sun' tries to do that, the NFVCB stands in the way," Ike Anya wrote on the film's Facebook page.