Rwanda police justified the arrest of the former presidential hopeful, saying Diane Shima Rwigara had failed to respond to previous summonses. She had been barred from standing in the August elections.
A police spokesman said Rwigara and her mother and sister were arrested on tax evasion charges in Kigali on Monday.
"They are accused of tax evasion and secondly Diane Rwigara is accused of using fake documents while she was gathering signatures for (her) presidential candidacy," police spokesman Theos Badege told reporters on Monday. He said Rwigara had failed to respond to three summonses.
Election authorities claimed Rwigara had not submitted the required number of supporters' signatures and that some of the names she presented were those of dead people. The 35-year-old accountant's name did not appear on the ballot after the election board said she did not have enough support.
President Paul Kagame won the elections with nearly 99 percent of the vote after a constitutional change opened the way for him to stand for a third term. Rwigara has spoken out against the president, accusing him of bad governance, and about injustice and oppression.
"Tell us why we are being arrested? Why should we go to the police while you have confined us to this place and took away all our money without leaving us any?" Rwigara said as she and her family were being taken away. She claimed she had been held under house arrest before police arrived on Monday evening.
In a comment on her Twitter account, Rwigara claimed "police staged a fake forced entry" into the house:
Spokesman Badege said police had searched Rwigara's home and taken a few items and money away, but in line with a clear application of the law. Police claimed they had arrived at the house, jumped over the gate and found the three accused hiding in the annex of their house.
Rwigara's father, the businessman Assinapol Rwigara was killed in a car accident in February 2015, which his family believes was a politically motivated murder. He had been a key financial backer of the Rwandan Patriotic Front, the ruling political party now led by Kagame.
Rwigara has accused Kagame of stifling dissent and his party of keeping a near total hold on power.
Former guerrilla leader Kagame was praised for leading a government which brought stability and growth following the 1994 genocide, when an estimated 800,000 people were killed in inter-ethnic violence between Tutsi and Hutu communities.
While there has been dissent over the lack of job opportunities, Kagame appears popular in Rwanda which has seen economic growth and stability.
jm/bw (Reuters, AFP)