Ugandan opposition leader Bobi Wine was arrested on Monday during a protest in Kampala, according to a statement released on his Twitter account.
"Bobi Wine arrested as he led MPs and other leaders in a peaceful protest against the abduction, torture and murder of his supporters. The protest was taking place at City Square, Kampala," read a statement released by the administrators of his account.
Last week, Mr Wine urged supporters to demonstrate in Kampala, prompting authorities to send security personnel to the capital.
The pop star turned opposition leader claims hundreds of his supporters were seized and some tortured by state agents.
"Ugandan authorities should take immediate steps to end the ongoing abductions by suspected state agents and cease the unlawful detention without trial of opposition supporters," Human Rights Watch said in a statement.
The rights group said witnesses described to investigators how non-uniformed armed men picked up people from streets and homes and shoved them into vans without license plates.
Some victims said their abductors beat and detained them in unmarked buildings for grilling over their political affiliation and involvement in protests.
"The recent spate of enforced disappearances has only compounded the intense climate of fear in Uganda following the recent violent national elections," said Oryem Nyeko, Africa researcher at Human Rights Watch.
This month, Mr Wine's National Unity Platform released a list of more than 400 supporters it said were still missing or had been released after abduction, some bearing torture marks.
Mr Wine, 39, whose real name is Robert Kyagulanyi, lost to Yoweri Museveni in a Jan. 14 presidential election marred by widespread violence. He rejected the results, claiming he won.
The opposition leader was held under house arrest from polling day until a Ugandan court ordered him to be freed about two weeks later. Security forces barricading his house were ordered to step down.
"It has been an experience of isolation, of torture, of humiliation, having our compound turned into a military garrison," Mr Wine had told Reuters.
Mr Museveni's government says Mr Wine is trying to destabilise Uganda via violent and illegal protests.
