Museveni, who is seeking re-election on his National Resistance Movement (NRM) party ticket, said the move was necessary because some people were using Facebook, Twitter and WhatsApp to peddle lies.
“Steps were taken to stop so many (social media users from) getting in trouble; it is temporary because some people use those pathways for telling lies,” he told journalists shortly after casting his vote in the western Kiruhura district.
The Uganda Communications Commission (UCC) cited an unspecified national security reason for the shutdown at around 8 am, an hour after voting began.
UCC’s director of corporate affairs Fred Otunnu said “we have switched off but only temporarily because as you know this is a very sensitive period”.
WhatsApp, a popular instant messaging service that can be accessed by everyone using a smartphone, was shut down as early as 9am, and was closely followed by mobile Facebook.
Mobile Telecommunications Network (MTN), the leading mobile service provider in Uganda, posted on its Twitter page that the UCC had ordered the company to take down the sites and disable the mobile money transfer platform.
“The UCC has directed MTN to disable all social media & mobile money services due to a threat to public order & safety,” the company stated.
Being Internet-enabled, social media platforms can be tampered with or blocked by governments. Last year, for example, a judge in Brazil ordered the switch-off of WhatsApp for 48 hours after Facebook turned down the government’s request to eavesdrop on users' messages.
Meanwhile, Uganda Electoral Commission chairman Badru Kiggundu extended the deadline for voters to turn up at polling stations from 4pm to 7pm. Kiggundu said the extension had been prompted by the electoral body's earlier delay in delivering voting materials to various polling stations across the country.
Ugandan police had fired tear gas to disperse furious voters in the capital Kampala as the election commission apologized for the hours-long delays in delivering ballot papers, AFP reported.
Voting was due to begin at 7 am, but was stalled for several hours in some polling stations in the city and surrounding Wakiso district when ballot boxes and papers did not arrive on time.
The capital traditionally shows strong support for the opposition. "There has been a delay in delivery of polling materials in some parts of Wakiso district and Kampala capital city. The Electoral Commission regrets the delay," the commission said in a statement.
"The polling materials have now been delivered to all these places and polling has commenced in most of the places," the statement added.
Besides Museveni, other top candidates in the race include FDC’s Kizza Besigye, a four-time presidential aspirant, and former prime minister Amama Mbabazi.