Story highlights Authorities say a leading opposition leader, Kampala's mayor and a ruling party candidate are arrested

President Yoweri Museveni says social media shutdown is "to avert lies ... intended to incite violence"

Museveni is running for a fifth term, and has been president for 30 years

(CNN) Tensions mounted as votes in Uganda are counted in an election that saw the detention of the leading opposition candidate, a ban on social media and allegations of voter fraud.

Ugandans voted on Thursday on the fate of President Yoweri Museveni, who is hoping for a fifth term after ruling the nation for the last 30 years.

The day began with many politically-minded voters unable to tweet or update their Facebook pages after a government ban on social media.

After casting his vote at his home in western Uganda, Museveni defended the ban as a "security measure to avert lies ... intended to incite violence and illegal declaration of election results."

Human rights groups condemned the social media clampdown. Many citizens accessed social media sites via encrypted private networks. A similar shutdown occurred during the 2011 general election.

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