Shiite Muslim leader Ibrahim Zakzaky and his wife detained for murder since 2015 in Nigeria have on Wednesday been discharged, lawyers said.

The prominent cleric has been at loggerheads with the secular authorities for years because of his calls for an Iranian-style Islamic revolution in Nigeria, where Shiites make up a small minority.

Zakzaky, his wife Zeenah Ibrahim and 200 of their followers were arrested in a violent crackdown in the northern city of Zaria.

A court in 2016 ordered the couple be released -- but the authorities ignored the demand and filed charges against the cleric including the murder of a soldier.

"None of the 15 prosecution witnesses proved they committed the offence," lawyer Sadau Garba told AFP after Wednesday's hearing, adding that the couple had been acquitted and "regained their freedom today."

Lead prosecutor Dari Bayero confirmed that the pair had been freed but said the state was planning to appeal.

"The court ruled that none of the witnesses we presented in court gave convincing proof that the duo were guilty," Bayero said.

"This doesn't mean they can't be re-arraigned... we are certainly going to file charges against the duo at appeal."

Amnesty international urged the Nigerian authorities to "immediately comply" with the court order.

"If the government once again deliberately disregards the orders of its own courts, it will demonstrate a flagrant -- and dangerous -- contempt for the rule of law," the rights group said in a statement.

Troops launched a ferocious clampdown on Zakzaky's group, the Islamic Movement in Nigeria (IMN), in December 2015, when members blocked the convoy of the army chief of staff during a religious procession.

Rights groups said at the time that some 350 IMN members were killed during two days of clashes and later buried in mass graves.

Hundreds of supporters of Shiite Muslim leader Ibrahim Zakzaky demonstrate in Abuja, on July 10, 2019, to demand his release Hundreds of supporters of Shiite Muslim leader Ibrahim Zakzaky demonstrate in Abuja, on July 10, 2019, to demand his release Photo: AFP / Kola SULAIMON

The army initially denied the events and said a soldier was killed by armed Shiites.

Zakzaky's continued detention has led to street protests in the nation's capital Abuja, sparking violent clashes with security forces that have claimed dozens of lives.

The Nigerian government officially outlawed the group in 2019.

That same year, 100 of the detained members were released in two batches after a court acquitted them.

And in February last year another court released 87 other IMN members for lack of evidence.

After the announcement of Zakzaky's release, his lawyer said the cleric and his wife "now need to go home, have some rest and attend to their urgent medical needs."

But he added they will "seek damages against the Kaduna state government for all the deprivations and the travails our client suffered."

A spokesman for the IMN, Ibrahim Musa, said the court's decision was "a victory for truth and justice against tyranny and impunity".

"The false charges filed against them have finally been punctured for good after almost five years of excruciating illegal detention," Musa said.

"This judgement has not only vindicated them and all members of the Islamic movement in Nigeria, but it is certainly a victory for perseverance in the face of extreme persecution by the Nigerian government."