The Nigerian government has declared the separatist group, the Indigenous People of Biafra (Ipob), a terrorist organisation.
The country’s army had made a similar declaration last week but it later retracted the statement.
Now the government says it has obtained a court order permitting it to declare Ipob a terror group.
Ipob is demanding an independent state in south-east Nigeria.
Nigeria’s Justice minister Abubakar Malami told the BBC that the court order criminalises Ipob and is intended to ensure no member of Ipob operates within Nigeria.