Amnesty Internationalinfo-icon on Monday urged Nigeriainfo-icon to comply with a courtinfo-icon ruling to release a pro-Iraninfo-icon cleric and hundreds of his supporters, as a deadline for them to be freed loomed.

Ibrahim Zakzaky, who leads the Shiainfo-icon Musliminfo-icon Islamic Movement of Nigeria (IMN), has spent more than a year in custody since clashes between his followers and troops.

The three days of violence in the northern city of Zaria left at least 350 IMN members dead, according to human rightsinfo-icon groups. Nigeria's military has rejected the claimed death toll.

A judge in Abuja on December 2 called the detention of Zakzaky and his followers illegal and unconstitutional, and imposed a 45-day deadline for their release, which expires later on Monday.

Amnesty Nigeria director Makmid Kamara said the government "will demonstrate a flagrant -- and dangerous -- contempt for the rule of law" if it ignored the ruling.

"Zakzaky is being unlawfully detained," he said in an emailed statement.

"This might be part of a wider effort to cover up the gruesome crimes committed by members of the security forces in Zaria in December 2015 that left hundreds dead."

There was no immediate response from the government.

The IMN and Zakzaky have been at loggerheads with the federal government for years, not least because he has called for an Iranian-style revolution in Nigeria.

The Kaduna state government in December said Zakzaky should be "held responsible, fully investigated and prosecuted" for "acts of lawlessness committed by the organisation" over the last 30 years.

Nigeria is constitutionally secular but religiously divided between a mainly Christian south and largely Muslim north, which is predominantly Sunni.