Abuja - An activist campaigning for a separate state of Biafra in southeast Nigeria is being investigated for "terrorism and terrorism financing", his lawyer said on Monday.
Nnamdi Kanu, whose arrest last month has sparked a wave of protests, is already charged with criminal conspiracy and intimidation as well as membership of an illegal organisation.
Kanu is the director of Radio Biafra, which the government has accused of being "seditious" and of broadcasting "hate speech", and a founder of the banned Indigenous Peoples of Biafra (IPOB) group.
He was brought to a magistrates court in the capital on Monday following a ruling last week when Nigeria's secret police, the Department of State Services (DSS), failed to produce him.
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But proceedings were adjourned until December 1 after the prosecution asked for the case to be tried in a higher court.
Kanu's lawyer, Vincent Egechukwu, told reporters the DSS had secretly obtained an order at the Federal High Court on November 10 for his continued custody.
The order enables the DSS "to detain (Kanu) in its custody for a period of 90 days pending the conclusion of an ongoing investigation of terrorism and terrorism financing", he said.
Kanu has denied the original charges and was previously granted conditional bail but the DSS refused to release him, arguing the conditions for his release had not been met.
Kanu, who has emerged as the new figurehead for Biafran separatists, came to court dressed in a light-blue shirt with a white collar and sleeves rolled up to his elbows.
He was surrounded by dozens of armed security men but waved and smiled to well-wishers outside the court. Afterwards, he was whisked away in a security vehicle.
Pro-Biafran activists have renewed their claim for a separate state, arguing the southeast region has been neglected by a succession of federal governments since the end of the civil war.
The conflict from 1967 to 1970, which left some one million dead mainly from starvation and disease, was sparked when Biafran leaders unilaterally declared independence from Nigeria.