The opposition party of Ugandan presidential challenger Bobi Wine said that police have prevented top officials from going to their headquarters in the capital, Kampala, as they prepare to launch a legal challenge to free Mr Wine from house arrest.

Police swooped in at dawn at the offices of Mr Wine’s National Unity Platform, diverted traffic, and stopped people from entering, party spokesman Joel Ssenyonyi said.

Mr Wine, whose real name is Kyagulanyi Ssentamu, was the main opposition challenger in presidential elections last week that electoral authorities say long-time leader Yoweri Museveni won with 58% of the vote.

Mr Wine, who took 34% of the vote, has rejected the official outcome as fraudulent and insists he will use all legal means to protest the allegedly “cooked-up” results.

Mr Wine’s party has said it has video evidence of the military stuffing ballot boxes, casting ballots for people and chasing voters away from polling stations.

Opposition politician Medard Sseggona, a lawyer for Mr Wine, said he feared police would seize any vital information related to the elections that was kept at the party’s headquarters.

Mr Museveni has dismissed the claims of vote-rigging.

“I think this may turn out to be the most cheating-free election since 1962,” when Uganda won independence from Britain, said Mr Museveni in a national address.

But the election was marred by violence ahead of polling day as well as an internet shutdown that remained in force until Monday morning, when access was restored for most Ugandans, although social media sites remained restricted.

Mr Wine has been effectively under house arrest since he cast his vote and now is allegedly unable even to receive visitors.

Police thwarted opposition officials who were trying to meet with Mr Wine at his home outside Kampala in order to discuss the way forward, Mr Ssenyonyi said.

Politician Francis Zaake has been taken to hospital after allegedly being assaulted by police who denied him access to Mr Wine’s house.

Mr Wine’s party will seek a court order to end Mr Wine’s apparent house arrest, Mr Ssenyonyi said.

“His home is not a detention facility,” he said.

Police spokesman Fred Enanga said security forces are “maintaining a security presence” around Mr Wine’s home as a pre-emptive measure against possible rioting in the aftermath of the disputed polls.

Mr Wine is allowed to leave his home under “escort” in order to prevent his followers from “instigating riots and violent demonstrations”, he said.

Police similarly surrounded the home of opposition candidate Kizza Besigye after presidential elections in 2016, preventing him from going out after the official results of his loss to Mr Museveni had been declared.

Mr Wine has said his campaign against Mr Museveni is nonviolent and that his followers are unarmed.

In a generational clash watched across the African continent with a booming young population and a host of ageing leaders, the 38-year-old singer-turned-politician posed arguably the greatest challenge to Mr Museveni, 76, since he came to power in 1986.

Calling himself the “ghetto president”, Mr Wine had strong support in Uganda’s cities, where frustration with unemployment and corruption is high.