KAMPALA - Social media has been blocked in Uganda because of security concerns as tightly contested presidential elections are held, officials say.
Mobile money services had also been shut to make sure they would not be used to bribe voters, they added.
However, many users have found a way around the controversial restrictions.
President Yoweri Museveni, 71, is seeking to extend his 30-year rule, in a race widely seen as the tightest in the East African state's history.
His main challenger is his former physician, Kizza Besigye.
He has said he does not think the election will be free and fair.
Former Prime Minister Amama Mbabazi is also seen as a leading contender for the presidency.
The head of Uganda's media regulator, Godfrey Mutabazi, said the block was introduced after a request from the electoral commission, local media reports.
Uganda's leading mobile operator MTN, which has 10 million users, confirmed that it had received an order to shut down social media services, which include WhatsApp, Facebook and Twitter.
Despite the attempt to restrict the use of social media, #UgandaDecides is still trending on Twitter.
The election has been marred by delays of up to five hours at some polling stations.
The electoral commission said difficulties in transporting electoral materials caused the delays.
It added that despite the delays, voting will not be extended.
The BBC's Catherine Byaruhanga in the capital, Kampala, reports that thousands of people who had queued for hours got visibly frustrated over the delays.
Security forces were sent in to calm the situation, she adds.