Uganda's main opposition figure has been arrested ahead of the inauguration Thursday of the country's long-time president.

Patrick Onyango, a spokesman for Ugandan police, said Kizza Besigye, who claims he won the presidential election held in February, was arrested Wednesday as he addressed a crowd of supporters in the capital, Kampala.

There are fears of violence as the police try to foil possible protests Thursday when President Yoweri Museveni is to be sworn in. On Wednesday social media sites like Facebook and Twitter appeared to have been shut down by a government censor.

In addition to Besigye, other opposition figures have been detained inside their homes since Monday, in what police say are measures to prevent them from committing crimes.

Museveni has held power here since 1986.