Supporters of an imprisoned Shiite cleric on Wednesday said they had begun burying dozens of people they say were killed in clashes with the Nigerian security forces.The Islamic Movement of Nigeria (IMN) said 49 of its members lost their lives since Saturday, contrasting the military's official death toll of six. The army and police fired live bullets at crowds who marched near and in the capital, Abuja, protesting for the release of IMN leader Ibrahim Zakzaky, who has been in custody since 2015.In Mararaba village, in Nasarawa state just over the border from the Federal Capital Territory, mourners gathered in preparation for the burial of 20 victims.AFP reporters counted the white-shrouded bodies, as IMN members and tearful family members of the deceased gathered to pay their final respects."These are the victims the Nigerian Army attacked on Monday at Kugbo security check point on our way to Abuja," said IMN member Abdullahi Mohammad Musa.The group's spokesperson, Ibrahim Musa, said separately that another burial for six people was held in the northern city of Zaria. "We are feeling bad, we are feeling wronged, we are oppressed," he added.Nigeria, Africa's largest economy, is almost evenly split between a mostly Muslim north - which is predominantly Sunni - and a largely Christian south. Experts have warned the government that a heavy-handed response to the group risks sparking conflict in a volatile region where poverty is widespread. The December 2015 clashes that led to Zakzaky's detention saw the army kill more than 300 of his supporters, who were buried in mass graves, according to human rights groups.The latest clashes and the military's use of deadly force against civilians have raised fears that the IMN could become radicalised in the same way as the Islamist group Boko Haram in northeast Nigeria, who were subject to a crackdown in 2009.The military offensive against the jihadist group is widely accepted as the catalyst for it to take up arms against the government. Conflicting death tolls are not unusual in Nigeria and the authorities often play down casualty figures.Nigeria's Army said troops fired on IMN in self-defence.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook. "They met the soldiers in the call of their duty and the soldiers tried to defend themselves," said defence spokesperson John Agim.On Saturday, the military fired at the IMN procession and accused them of attempting to steal weapons and ammunition, an account the IMN "categorically" denies. Two days later, IMN and troops clashed again on the outskirts of Abuja. The Shiite group said 36 people died after the army shot into the crowd. On Tuesday, Nigerian police fired shots and tear gas at the supporters during another march and arrested 400 IMN members.Zakzaky is currently facing a culpable homicide charge in connection with the 2015 violence and is in jail despite a court order granting him bail.The Shiite leader, who is in his mid-sixties, has been at loggerheads with the authorities for years because of his call for an Iranian-style Islamic revolution in Nigeria.