A pro-Iranian cleric who has been in Nigerian custody since clashes between troops and his followers in December 2015 is facing fresh criminal charges, according to court documents seen by AFP on Friday.Ibrahim Zakzaky and three other leaders of the Shiite Muslim Islamic Movement of Nigeria (IMN) face eight criminal charges in the case filed on April 18 in the High Court of Justice of Kaduna State. Along with culpable homicide that is "punishable with death", Zakzaky is accused of unlawful assembly and disturbing the peace. According to court documents, his supporters were armed with dangerous weapons -- such as pistols, cutlasses and axes -- and killed a soldier.IMN spokesperson Abdullahi Yola told AFP the charges were "absurd"."Why is it that the charges keep coming after keeping the Sheikh (Zakzaky) in an illegal detention for two and a half years?" he asked.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and FacebookZakzaky has been in government custody since the bloody clash in the northern city of Zaria, despite court orders that he should be freed.Rights groups have accused Nigeria's military of killing more than 300 IMN supporters and burying them in mass graves during the 2015 confrontation, a charge they deny. Zakzaky has been at loggerheads with Nigeria's secular authorities for years because of his call for an Iranian-style Islamic revolution. Northern Nigeria is majority Sunni Muslim.Zakzaky, who is in his mid-60s and lost the sight in one eye in the 2015 clashes, made a rare public appearance in January to counter rumours he had died. He was seen at the offices of Nigeria's intelligence agency wearing a neck brace and walking with the aid of a stick.His supporters have held a series of protests in Nigeria's capital of Abuja in recent weeks to demand his release and have had a series of standoffs with police.That led to the arrest of over 100 IMN members.