Uganda's opposition leader was briefly arrested as the country wrapped up voting in a presidential election his supporters claim was rigged in favour of long-time leader Yoweri Museveni.

Al Jazeera witnessed police detaining Kizza Besigye, the main opposition candidate, as he and his supporters tried to show journalists what they said was a vote-rigging operation in a suburban house.

When Besigye's supporters turned up at the house, several people fled before fighting with the opposition members, who then held them at the scene.

The men were carrying guns stamped with police insignia and they also had handcuffs.

Besigye demanded that he be allowed into the house to check for vote-rigging, and was then arrested.

Police later told Al Jazeera that the building was an intelligence facility.

Earlier, police fired tear gas at voters furious about delays at polling stations. Voting was scheduled to begin at 7am local time, but was held up for hours in several polling stations in the capital, Kampala, and the surrounding Wakiso district after ballot boxes and papers did not arrive on time.



Kampala traditionally shows strong support for the opposition.



"There was a bit of a delay at some polling stations because of logistical problems," Jotham Taremwa, an election commission spokesman, said.



At one Kampala polling centre, hundreds of frustrated voters shouted and gesticulated at election officials. "They are denying us our constitutional right," said Elias Bukenya, a 27-year-old teacher who suspected foul play. Social media, including Facebook and Twitter, were largely inaccessible on voting day, although internet-savvy Ugandans dodged the apparent shutdown using virtual private networks.

The government regulator, the Uganda Communications Commission, said the shutdown was for "security reasons".

Museveni, a former rebel who seized power in 1986, is widely expected to win a fifth term, which would extend his power into a fourth decade.

Elections in 2006 and 2011 were marred by violent and occasionally deadly street protests and a liberal use of tear gas by heavy-handed police. But, apart from an outbreak of protests when police prevented Besigye from campaigning in the centre of Kampala, campaigning was mostly peaceful. "Whoever will try to bring violence, you will see what we shall do to him. Those who want violence should play somewhere else, not Uganda," Museveni told thousands of supporters in his final rally on Tuesday. Some who attended that rally told Al Jazeera that they had been paid about $1 to be there. The NRM, the governing party, denies that it pays people to attend political events. Besigye, who has contested the presidential election three times, says he is confident of a first-round win. READ MORE: Fear and hope surround Uganda's elections

"The voice from the people is that they have been failed in the last 30 years, and what could not be done in that long period, could not be done in another five years," he said. Voter turnout has followed a downward trajectory in recent elections, with nearly three-quarters of eligible voters casting a ballot in 1996, during the country's first competitive election. However, only three-fifths bothered to turn out in 2011. Museveni's share of those votes has also declined but most 2016 opinion polls give him more than the 50 percent needed to avoid a run-off. He won his last five-year term in 2011 with 68 percent.

The other main challenger, Amama Mbabazi, a former prime minister and ruling party stalwart, has also accused the NRM of planning to stuff ballot boxes.

"My main worry is the use of state machinery to support one candidate against all the laws," Mbabazi told Al Jazeera.

"And, two, the planned interference with the electoral process and the possibility of rigging."

Ofwono Opondo, a government spokesperson, dismissed the claim as the "cry of a loser", according to the country's Daily Monitor newspaper.