Rwanda's most prominent opposition leader, Victoire Ingabire, has been arrested.
Police say she was implicated in an investigation into the activities of an ex-commander of a Hutu militia group.
Ms Ingabire returned from exile in January to challenge President Kagame but she was barred from standing in the August election.
She still faces charges from a previous arrest in April.
At that time she was accused of collaborating with a terrorist group and denying the genocide in 1994.
Ms Ingabire, leader of the FDU-Inkingi party, is a Hutu and most of those killed in the 1994 conflict were ethnic Tutsis.
Police spokesman Eric Kayiranga said that on Wednesday, Major Vital Uwumuremyi, a former commander in the FDLR Hutu militia, was arrested on charges of forming a terrorist organisation.
The FDLR - Democratic Forces for the Liberation of Rwanda - operates in the east of the Democratic Republic of Congo.
Mr Kayiranga said the UDF leader was arrested from her home in Kigali "after investigations revealed that the charges against Major Uwumuremyi implicate Ms Ingabire".
Both are being held at Kicukiro Police Station.
Human rights groups have accused the Rwandan government of using terrorist allegations to stifle opposition in the country.