The former President of Comoros, Ahmed Abdallah Sambi has been taken into custody amid an investigation into an economic citizenship programme introduced by his government, his family says.
He has been under house arrest since May and denied access to phones and computers.
But an investigating judge has now ordered he be formerly detained.
Mr Sambi denies the accusations levelled at him linked to money that has allegedly gone missing from a scheme to sell passports to fund development.
Observers say his arrest came amid a crackdown on opponents of constitutional reforms on the Indian Ocean archipelago.
Last month, the opposition called for a boycott of a referendum on changing the constitution to stop the rotation of the presidency between the islands every five years.
The successful “yes” vote means current President, Azali Assoumani can seek another five-year term.