Ugandans have begun voting in a presidential election that is expected to extend Yoweri Museveni's term in office to three decades.
Opposition parties in the country, however, have threatened that if the polls are deemed to have been rigged, they will take to the streets.
Museveni has given warning that large-scale protests such as those being threatened will not be tolerated, and anyone taking part will be arrested.
The elections come after a bitter election campaign in east Africa's third largest economy. There have been widespread allegations that Museveni's party has been paying voters to back him for a fourth term.
Kizza Besigye, the opposition front-runner, has already lost two previous elections to Museveni, a former ally.
Many Ugandans complain of rampant corruption and a lack of investment in basic public services and infrastructure under Museveni, but others respect him for bringing stability to the country.
One of the major issues on the agenda for whoever wins the election will be managing the country's newly discovered oil reserves, which are estimated to be in the billions of barrels.
The country's last two elections, in 2001 and 2006, ended in dispute, after Besigye unsuccessfully appealed to the supreme court both times to overturn the results.
The time, he says that he is producing his own results tally, and if it does not match the official outcome, he has threatened mass protests.
"If the electoral commission releases results that we know to be fraudulent, at that stage we shall recommend the Ugandan people deal with the matter directly," Besigye said earlier this week.
Museveni appeared confident in the lead-up to the polls, however. "It will be a big win," he said on Wednesday.
His government has deployed thousands of security-forces personnel to oversee the holding of elections, and he has cautioned bodies other than the electoral commission against declaring results.
Suspicions of rigging were already rife on Friday, particularly in the Rubaga area, an opposition stronghold. Voters there said that ballot papers had not been delivered to polling stations by the time that voting was due to start.
Polling stations across the capital, Kampala, also reported delays, though election observers have said that millions had voted by late on Friday morning.
European Union observers said voting had so far been peaceful, but were concerned some voters were being turned away from polling stations despite being registered and that they had seen a number of improperly sealed ballot boxes.
The EU's chief observer, Edward Scitluna, said that in three out of five polling stations visited by midday ballot boxes had not been sealed correctly and their lids could be lifted.
"My impression is that's a lack of training, not systemic rigging," said Scitluna, adding some voters were being told they had not registered despite thinking otherwise.
Voters in the village of Wii-Aworanga said candidates from all parties had offered bribes of up to 100,000 shillings ($40) per village ahead of the election to secure votes.
"Bribes came from everybody ... but of course the NRM (ruling National Resistance Movement) are the government and they offered more," one voter who did not want to be named told Reuters news agency.
Al Jazeera's Mohammed Adow reporting from Kampala said the voting has gone well in most places but in eastern Uganda there were clashes between two opposing candidates in one of the parliamentary constituencies.
"Supporters of the minister of defence and supporters of her opponent clashed in and around the town of Mbale," he said.
"Two people are confirmed dead and up to 30 injured, including a journalist. The military has been deployed to quell the situation."
Analysts have said that a public uprising is unlikely to succeed in Uganda, where the population is less educated and has less access to the internet than in Egypt, which Besigye cited as being the kind of uprising Uganda would witness.
Polls are expected to close at 1400 GMT. The country's electoral commission says it will announce the results within 48 hours of the polls closing.
Source: Al Jazeera and agencies