Rwandan Human rights activist Diane Rwigara who was disqualified from last election, now faces treason charges, the newspaper The East African reports.
It also reports that she is facing charges for inciting revolt and revealing “sensitive information”.
Ms Rwigara, who was arrested on Friday, has been under investigation over alleged forgery.
Authorities have also investigated her family over alleged tax evasion.
Police spokesperson Theo Badege said in a statement on Sunday that Ms Rwigara had been arrested for failing to co-operate with the police:
The decision to arrest was in addition to the behaviour of the suspects during preliminary investigations, particularly their consistent refusal to co-operate with the police and publicly revealing information that is, by law, supposed to be confidential.”
The criminal procedure law gives investigators powers to detain a suspect for a maximum of five days in order to conclude investigations and decide, based on the evidence, whether or not to forward the case to prosecution.”
Ms Rwigara has previously denied working with exiled opposition groups, it adds.
Ms Rwigara was disqualified as a candidate in last month’s presidential race which was won by incumbent President Paul Kagame.
Investigators allege that Ms Rwigara committed an electoral offence by collecting forged signatures to endorse her candidacy.