JOHANNESBURG -- Rich in the minerals that power the world's mobile phones and laptops, yet desperately underdeveloped, Congo votes on Sunday for its first new president in nearly two decades. This could be the sprawling country's first peaceful, democratic transfer of power.

But a last-minute decision to bar some 1 million voters because of an Ebola virus outbreak , after two years of various election delays, has angered many. The opposition worries manipulation of controversial voting machines could ensure that President Joseph Kabila's preferred successor wins. Here's a look at the troubled election.

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WHO'S RUNNING?

The three top candidates were relative unknowns even months ago.

Kabila has put forward loyalist Emmanuel Ramazani Shadary as the ruling party candidate. The former interior minister is under European Union sanctions for a crackdown on Congolese who protested the delayed election. Congo's annoyance over the sanctions has worsened relations with the West, whose observers have not been invited to watch Sunday's vote.

Kabila, blocked from serving three consecutive terms, has hinted he'll run again in 2023, leading the opposition to suspect he'll wield power behind the scenes until then to protect his vast wealth.

The opposition is split after briefly uniting behind leading candidate Martin Fayulu, a businessman and lawmaker in Kinshasa, the capital. Felix Tshisekedi, son of late opposition icon Etienne and head of Congo's most prominent opposition party, broke away to join forces with the party of Vital Kamerhe, who finished third in the 2011 election.

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WHY THE LATEST UNREST?

Congo's electoral commission made a surprise decision on Wednesday to bar some 1 million people in two eastern cities from voting on Sunday, blaming an outbreak of the deadly Ebola virus. They will vote instead in March, months after the new president is inaugurated in January. The decision has been criticized as undermining the credibility of the election.

Protests erupted in Beni and Butembo as residents demand to vote with the rest of the country. Health officials have said precautions were in place to allow safe voting, with electoral officials involved. "If they knew there wouldn't be an election here, why did they instruct candidates to campaign?" one Beni protester said.

The International Rescue Committee, among aid groups forced to suspend their work, accused Congo's electoral commission of using the outbreak "as a political ploy, putting aid workers in immediate danger." It noted the cities have a large number of opposition supporters.

The Ebola outbreak, declared in August, is the second-deadliest in history and the most complex. Response workers face rebel attacks and community resistance in a region that had never faced Ebola before. Residents are bitter that the government now claims to protect them from the virus after failing to protect them from rebel attacks that have killed 1,500 people in Beni alone in the past four years.

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IS CONGO READY TO VOTE?

Voting machines, used for the first time in Congo, have been questioned for months. Just 9 percent of the largely rural country has electricity. Many of the country's 40 million voters have never used a computer, but the electoral commission expects people to take less than a minute to navigate a touchscreen and select a president and local representatives.

The opposition has asked mobile phone providers to disable the machines' SIM cards, saying they could transmit election results with no transparency while results are meant to be printed and counted by hand.

Some Congolese observers in the past week said voting materials still had not been delivered to polling stations. In some remote areas, machines must be carried on foot through bush or jungle to polling stations. Even in Kinshasa less than 48 hours before the vote, several people trained to be polling agents told The Associated Press they had yet to see the machines.

The electoral commission insisted everything is ready.

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