A Ugandan activist, one of dozens detained this week for participating in banned demonstrations, was sexually assaulted in custody, his lawyer has said.
More than 90 youths were arrested and some were charged with being a public nuisance following anti-corruption protests that hit the capital, Kampala.
Some of those released from detention have also reportedly said they had been sexually assaulted while in police cells, sparking widespread criticism. But police denied the allegation.
"He was sodomised immediately after he was detained. The police think that gays are funding the protests... they told him 'now you earn it'," lawyer Eron Kiiza said to the BBC.
The march was organised on social media amid anger over long-running allegations of corruption involving several high-profile public officials.
The protesters, inspired by anti-tax demonstrations in Kenya, were demanding the resignation of the parliamentary speaker, who has been accused of corruption, which she has denied.
But the Ugandan riot police quickly stopped the protests, bundling several young activists, including a prominent TV presenter, into the back of lorries.
Some are facing a variety of charges but an unknown number remain in police custody, local media reported.
The security forces have been accused of violently cracking down on the protests.
Referring to the allegations of sexual assault, lawyer Mr Kiiza said while it was not common for people to be attacked like this in police cells "sometimes it happens to unfortunate people".
"It happens in the wake of desperation of some guys in the police [who are trying] to find a connection between the protests and the so-called foreign funders," Mr Kiiza added.
"It is like a revenge act."
The lawyer said he had medical documents that show the sexual abuse and he would use them to sue the authorities once his client is done with treatment and rehabilitation.
He declined to name his client and the cell the act happened, citing security fears.
Other activists, both male and female, were also sexually abused while in detention, opposition leader Bobi Wine has alleged.
"Only a few of them had the courage to publicly speak about their ordeal. Very many of them have reported to us but fear or feel ashamed to speak about it in public," Bobi Wine, a former pop star whose real name is Robert Kyagulanyi, added.
The allegation sparked uproar on social media with Ugandans calling for an independent investigation into the matter.
"If true, the people doing that may the Lord judge you!" Youth Minister Balaam Barugahara Ateenyi, posted on X.
The minister acknowledged that the allegations were dehumanising and said the country's police chief should investigate them.
The US embassy in Kampala said in a statement: "We urge that any allegations of individuals assaulted in detention be investigated and perpetrators be held accountable."
However, police spokesperson Kituuma Rusoke dismissed the claims as "unfounded" and "malicious".
"The police are very conscious of the rights of suspects and take their responsibilities seriously," Mr Rusoke added in a statement.
But President Yoweri Museveni praised the police for shutting down the protests, which he said were being funded by “foreign sources”.
Mr Museveni said “very bad things” would be revealed in court.
Amnesty International, a rights group, have called for an immediate and unconditional release of all those who were arrested.
“The heavy-handed tactics used by the Ugandan government to stifle and silence peaceful protesters show a manifest clampdown on dissent," it added in a statement.