ABUJA (Reuters) - Nigeria s armed forces said on Friday a group campaigning for the secession of a part of southeastern Nigeria formerly known as Biafra had been categorized as a  terrorist organization . The move follows days of tension in which members of the group accused the army of laying siege to their leader s home, which the army denied. A curfew was imposed in Abia state where the residence is located.  The Indigenous People of Biafra (IPOB) group has stepped up calls for secession since its leader, Nnamdi Kanu, was released on bail in April after being detained nearly two years on charges of criminal conspiracy and belonging to an illegal society. Secessionist sentiment has simmered in the region since the Biafra separatist rebellion plunged Africa s most populous country into a civil war in 1967-70 that killed an estimated one million people. The military presence in southeastern Nigeria has increased in the last few weeks as part of an operation that the military said was part of efforts to crack down on crime.  The Armed Forces of Nigeria wishes to confirm to the general public that IPOB from all intent, plan and purpose as analyzed, is a militant terrorist organization,  said armed forces spokesman John Enenche in an emailed statement.  The statement said IPOB had formed a  Biafra secret service  a paramilitary division, extorted money from people on public roads and attacked members of the armed forces.  An IPOB spokesman was not immediately available for comment.  The tension is another security challenge for President Muhammadu Buhari in addition to the eight-year Boko Haram jihadist insurgency in the northeast and attempts to maintain a fragile ceasefire in the southern Niger Delta energy hub. Militant attacks on oil facilities in the Niger Delta last year cut crude production by more than a third. Renewed calls for Biafran secession prompted Buhari to use his first speech after returning from three months of medical leave in Britain in August to say Nigeria s unity was  not negotiable .  Amid mounting tensions in the region, the army on Thursday said it was investigating video footage circulating on social media that purportedly showed troops at a checkpoint in Abia  using sticks to flog men stripped to the waist and forcing them to drink muddy water. Amnesty International in 2016 accused Nigeria s security forces of killing at least 150 Biafra separatists at peaceful rallies. The military and police denied the allegations. (This version of the story corrects typo in headline) 
Nigerian military labels Biafra separatist group a terrorist organization