Nigeria’s Appeal Court has dropped all charges against separatist leader Nnamdi Kanu after ruling that he had been illegally arrested abroad.
The court also ruled that his extradition had been illegal.
The ruling by a panel of three judges is seen as a major blow to the government which had detained Mr Kanu on various treason and terrorism-related charges.
He leads the banned indigenous People of Biafra (Ipob) group.
Ipob is campaigning for the creation of an independent state in south-eastern Nigeria.
Mr Kanu – who holds a UK passport – fled Nigeria in 2017 before he was seized and brought back in 2021.
His 2021 arrest abroad was illegal because extradition protocol was not followed, the court said.
Kenya has not commented on whether it played a role in Mr Kanu’s deportation to Nigeria.
The Appeal Court also ruled the Federal High Court did not have the jurisdiction to try Mr Kanu.
He initially faced 15 charges, but eight had previously been dropped.
He was originally arrested in 2015 but he fled Nigeria in 2017 while out on bail. He had previously denied any wrongdoing.
Ipob wants a group of states in the south-east of the country, largely inhabited by members of the Igbo ethnic group, to break away from Nigeria and form an independent nation called Biafra.
In 1967 Igbo leaders declared independence for the state of Biafra, but after a civil war, which led to the deaths of up to a million people, the secessionist rebellion was defeated.
But the idea of Biafra has never gone away and despite the arrests of his members, Mr Kanu’s movement has seen a recent swell in its numbers.