Uganda votes: Photo Malcolm Webb(Al Jazeera TV)

Ugandans started casting their votes on Thursday to decide whether to give Yoweri Museveni, in power for three decades, another term in office or oust him.

The voting came amidst unconfirmed reports  that phone networks have blocked usage of Twitter and Facebook.

Voting at most polling stations in the capital, Kampala, was yet to start 90 minutes after the official opening of polling at 7 am local time (0400 GMT), leading to concerns among some voters.

“If the voting time is reduced like this there will be many people who will not be able to vote,” said Dickson Mamber, a 34-year-old history teacher, who had been waiting in line for two hours at Muyembe polling station in Kampala.

Voting at the station still had not started by 0545 GMT.

All sides contesting the election accuse each other of stoking tensions and assembling vigilante groups, and the leading opposition candidates have predicted vote rigging.

Museveni, 71, has pleased Western allies by sending in peacekeeping troops to hotspots such as Somalia.

Besigye: Museveni’s main opposition

He faces two main challengers – longtime opposition leader Kizza Besigye, who has run unsuccessfully in three previous elections, and former prime minister Amama Mbabazi, who until recently was a close ally.

Besigye told Reuters on the eve of the vote Museveni was “not going to go peacefully” and said his supporters may stage street protests to dispute the election outcome.

Museveni meanwhile warned opponents to expect a tough response from security services if violence erupts.

The United States last week supported calls for a peaceful, transparent and credible vote.

Museveni, who came to power in 1986 after waging a five-year guerrilla war, is hailed by many Ugandans as providing decades of relative peace and economic stability. His rivals, however, are drawing strength from a clamour for fresh leadership.