"Our President (Bobi Wine) picked up by regime operatives as soon as he landed at the airport," David Lewis Rubongoya, the general secretary of Wine's National Unity Platform (NUP) said on X, formerly Twitter.
The post was accompanied by a photo appearing to show two men seizing the 41-year-old Wine by the arms on the tarmac at Entebbe International Airport.
Wine's supporters had planned to accompany him to his home north of the capital Kampala to welcome him back to the country, but police had said such a gathering was illegal.
Wine, a former popstar whose real name is Robert Kyagulanyi, is a prominent critic of President Yoweri Museveni and his government and has faced numerous arrests and alleged human rights abuses in the past.
Last month, Ugandan police announced they were banning rallies being organised by the National Unity Platform across the country because of public order issues.
Wine made a failed bid for the presidency in 2021 in a tense election against Museveni, who has ruled over Uganda with an iron fist since 1986.
The election campaign was marked by a crackdown on the opposition, and at least 54 people were killed during anti-government demonstrations.
Wine's return was eagerly anticipated by his supporters, many of whom view him as a symbol of change in a country ruled for so long by one man.
Ugandan soldiers and other security forces had been deployed on roads leading to Entebbe airport since early Thursday morning, as well as outside NUP offices and in Kampala's central business district.
Police had warned organizers not to go ahead with the planned procession and for people not to join the gathering, with police spokesman Patrick Onyango describing it as an "illegality."
Ugandan authorities have a long history of using so-called "preventative arrest" to detain opposition leaders, often holding them for several hours before returning them to their homes so as to stymie mass demonstrations.
Once hailed for his commitment to good governance, former rebel leader Museveni has crushed any opposition and tweaked the constitution to allow himself to run again and again.
The next presidential ballot is due in 2026. Museveni, 79, has yet to say if he will stand.
Forum