Nigerians have staged protest rallies in several cities to mark the 40th day after the army massacred hundreds of Shia Muslims in the northern city of Zaria.

The protesters in the northern city of Kano condemned the murder of the supporters of the Islamic Movement in Nigeria (IMN) on Saturday and called for the unconditional release of its leader, Sheikh Ibrahim al-Zakzaky.

Similar rallies were held in the cities of Zaria, Sokoto, Minna and Katsina to mark the massacre.

On December 12 last year, Nigerian soldiers attacked Shia Muslims attending a ceremony at a religious center in Zaria, accusing them of blocking the convoy of Nigeria’s Chief of Army Staff Lieutenant General Tukur Yusuf Buratai and attempting to assassinate him. The Shias have categorically denied the allegations.

One day later, Zakzaky was arrested during a raid by the army on his residence and the buildings connected to the Shia community in Zaria. Local sources say hundreds of people trying to protect the cleric, including three of his sons, were killed in the raid.

The Shia cleric is said to have been charged with “criminal conspiracy and inciting public disturbances.”

The IMN has called for Zakzaky’s unconditional release and for Abuja to respond to the “unjustifiable atrocities committed by the army.”

The IMN says it will continue the peaceful campaign to secure the release of Sheikh Zakzaky and other Shia detainees.

On December 16, 2015, the London-based Islamic Human Rights Commission (IHRC) said there was credible evidence of mass graves in Nigeria following the deadly attack on Shias.

The rights group said the Nigerian military had secretly buried hundreds of bodies in the graves after storming the house of the Shia cleric.

Human rights organizations have called for a full investigation into the deadly attacks by Nigerian forces against Shia Muslims.

On January 15, Amnesty International’s senior research adviser, Lucy Freeman, described the Nigerian army’s human rights violations as “shocking.”