A magistrate’s court in eastern Uganda has charged presidential candidate Robert Kyagulanyi, known as Bobi Wine, with the offence of committing an act likely to spread infectious disease.
During his court appearance, he said President Yoweri Museveni should be in court for murdering innocent civilians.
This comes after police said 37 people had died since Wednesday, when security forces responded to protests over the politician's arrest.
Human Rights Watch says it is clear that the Ugandan authorities are using Covid-19 guidelines as an excuse for violent repression of the opposition.
It says the governing party has been allowed to to continue campaigning without disruption despite also attracting large crowds.
It has called on the Ugandan government to ensure the security forces respect the rule of law, are impartial and are held accountable for abuses.