A leading member of a separatist movement in Cameroon has been taken into custody in the capital of neighboring Nigeria with his aides, sources and secessionists said on Saturday.

The once-fringe Anglophone movement in majority Francophone Cameroon has gathered pace in the last few months following a military crackdown on protests. It represents the gravest challenge yet to the 35-year rule of President Paul Biya, who will seek re-election this year.

Julius Ayuk Tabe, the Nigeria-based chairman of the Governing Council of Ambazonia separatist movement, was taken into custody alongside six others at a hotel in Abuja on Friday, said a Nigerian official and a member of the separatist group in Cameroon.