The man hoping to break Yoweri Museveni’s 30-year grip on Uganda’s presidency was briefly arrested on Thursday and the government shut down social media sites as voters cast their ballots under the gaze of police and soldiers in riot gear.
Opposition officials said Kizza Besigye was arrested at dusk and held for about 30 minutes in the capital Kampala.
All sides accuse each other of stoking tensions and assembling vigilante groups to intimidate rival candidates, and the leading opposition contenders predicted vote rigging.
Godfrey Mutabazi, head of the Ugandan Communications Commission, said Ugandan authorities had blocked access to Twitter, Facebook and WhatsApp services, citing security concerns.
Some voters in the capital area were frustrated by long delays at polling stations.
“Such a day is highly undermined by the lack of free and fair elections,” Mr Besigye (59) said.
Museveni (71) came to power in 1986 after a five-year guerrilla war and many Ugandans credit him with providing relative peace and stability. He is a staunch US ally.
After voting, he warned that anyone fuelling unrest would face the full force of the Ugandan security apparatus.
“If anybody tries to bring violence, we shall just get him, put him in the deep freezer until he cools down and . . . the blood pressure comes down,” he said.
Museveni was widely expected to win, although in urban areas young voters blame him for not tackling endemic corruption or creating jobs.