ABUJA (Reuters) - Police opened fire at Shi’ite Muslim protesters demanding the release of their leader in the Nigerian capital Abuja on Tuesday, killing one, in a second straight day of violence, the religious group said.

Troops had fired on a march on Monday by members of the Islamic Movement of Nigeria (IMN). The group said Monday’s shooting killed at least 24 protesters, but the military said only three people were killed and four soldiers were wounded.

On Tuesday, police attempted to stop hundreds of IMN members as they headed toward the center of Abuja, where most government buildings and the presidency are located.

They were demanding the release of their leader Ibrahim Zakzaky, who has been jailed since December 2015 when security forces killed hundreds in a crackdown on the group.

Zakzaky was charged in April this year with murder over the 2015 violence, after being held for more than two years. Nigerian authorities ignored a court ruling during the period before he was charged that the leader be released, sparking protests from his followers.

When marchers refused to turn back, police fired tear gas on the crowd. The protesters responded by hurling rocks, and the police opened fire, according to a Reuters witness.

As the violence escalated, at least one protester was killed, said Abdullahi Muhammed, an IMN youth leader.

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“The police they blocked the way, they started shooting tear gas and they used bullets,” he said, adding that the group was still trying to figure out how many were killed in Tuesday’s clash.

The Reuters witness saw at least one IMN member wounded by the gunfire and the protesters set ablaze a police car.

A police spokesman did not respond to calls and messages seeking comment.

IMN protests have frequently been met with force. In April, police fired bullets and tear gas during days of protests by IMN, wounding at least four protesters.

The repression of IMN, which is estimated to have three million followers, and the detention of its leader have drawn accusations from international rights watchdogs that President Muhammadu Buhari’s government is abusing human rights.

The crackdown has raised concern that IMN could become radicalized, in much the same way that the Sunni Muslim militant group Boko Haram turned into a violent insurgency in 2009 after police killed its leader.