Amnesty International has called on Ugandan authorities to drop treason charges against Kyandondo East MP Robert Kyagulanyi, popularly known as Bobi Wine.
In a statement, the rights body said the charges appear to be trumped-up against the opposition legislator.
The rights agency wants the charges dropped immediately and all brutal crackdown on opposition politicians ceased.
Besides Bobi Wine, 33 other opposition politicians have been charged with treason in connection with the clashes that took place between supporters of the ruling party and the opposition.
Opposition leader Kizza Besigye was also arrested on Thursday by police after surrounding his home in Kasangati for hours.
Besigye, a bitter rival of President Yoweri Museveni, was arrested as he attempted to leave his residence and taken to Naggalama Police Station.
"This appears to be little more than a witch hunt designed to silence political opposition in the country,” Amnesty International director for East Africa and the Horn and the Great Lakes Joan Nyanyuki said.
"These charges – for which no credible evidence has yet been produced – must be substantiated or dropped, and Bobi Wine released," she added.
Ugandan authorities on Thursday dropped court-martial charges against the outspoken musician cum-politician but immediately rearrested him.
He was later charged with treason at the Magistrate's court in Gulu District.
His continued detention without trial sparked protests in Uganda with activities and fellow opposition politicians calling for his release.
It was alleged that Wine was tortured while in detention.
On Thursday, Wine emerged for the first time in public since his arrest while supporting himself on crutches.
"This is a crude attempt by the Ugandan authorities to punish and stifle dissenting voices. The pattern of police aggression, mass arrests and the jailing of opposition political figures points to a systematic crackdown on those deemed to be challenging the authority of the President. It must stop."
Amnesty International called for prompt and impartial investigations into reports of deaths of people during Arua political campaigns and protests.
The protests were held to demand for the release of Bobi Wine.
The agency also called for investigations into the torture allegations against Bobi Wine.
"Any officers found to be responsible for these crimes must be held accountable," Nanyuki said.
Bobi Wine has been remanded till August 30 when his trial on treason charges is expected to commence.
Activists in Kenya on Thursday held protests outside the Ugandan Embassy in Nairobi demanding for his unconditional release.