Amnesty International said Monday that Ugandan security forces have used torture and arbitrary arrests to intimidate the opposition ahead of elections on January 15.
President Yoweri Museveni, 81, is seeking to extend his 40-year rule, but is accused of increasing repression to maintain power.
Amnesty said it had gathered evidence of security officers beating and using tear gas against supporters of the National Unity Platform (NUP), led by singer-turned-politician Bobi Wine, 43.
Wine also contested the 2021 election, which saw allegations of voting irregularities and state violence.
"The authorities have launched a brutal campaign of repression against the opposition and its supporters, making it extremely difficult for them to exercise their rights to freedom of association and peaceful assembly," said Tigere Chagutah, Amnesty's regional director for east and southern Africa.
An NUP supporter was killed at a rally on November 28.
Police said they were dispersing a violent crowd but the deceased's family told Amnesty they were barred from witnessing the postmortem process and were never given a death certificate.
Amnesty compiled a tally of 400 people arrested for supporting the NUP in recent months, on charges such as malicious damage to property or inciting violence.
Four interviewees told Amnesty they were beaten with batons, pepper-sprayed in the mouth, and tasered.
"They started pepper spraying us and pulled me out of the vehicle into a police truck," one interviewee, who did not give his real name, told Amnesty about a rally in the capital Kampala.
There are fears the government will shut down the internet during the election as they did in 2021 to prevent information spreading about voting manipulation and violence.
Imports of Starlink equipment were banned last month, and reports have spread in recent days that Elon Musk's company has agreed to a total block on its use in Uganda.
