Kenya held a rerun of its botched presidential election Thursday, but the opposition boycotted, and clashes broke out between police and protesters, threatening further political turmoil in one of sub-Saharan Africa's key economies.

The incumbent, Uhuru Kenyatta, was viewed as almost certain to win because of a boycott by the leading opposition candidate, Raila Odinga. Odinga had claimed that it was impossible to hold a credible election and told his followers that they now were part of a “resistance movement” against what he described as Kenyatta’s dictatorship.

In parts of Nairobi and western Kenya on Thursday, Odinga’s supporters engaged in running battles with police, lobbing rocks at officers who responded with tear gas and, occasionally, live bullets. At least four people were shot and killed by police.

In yet another blow to the electoral process, election officials announced Thursday that voting in four counties would have to be postponed until Saturday because of protests and violence. The delay extends a crippling period of uncertainty that already has ravaged the country’s economy.

Kenya has been seen as a maturing democracy and a key Western ally in a region troubled by war, undemocratic strongmen and an Islamist insurgency based in neighboring Somalia. But the past several months have cast doubt on the country’s political stability, with a widening gulf between two mostly tribal constituencies that have competed for power here for decades.

An opposition supporter reacts in front of a burning barricade in Mathare district on Oct. 26, 2017, as a group of demonstrators tried to prevent voters from entering a polling station. (Luis Tato/AFP/Getty Images)

In September, the Supreme Court annulled the results of the previous month’s presidential election, which had put Kenyatta on top by about 10 percentage points. It was the first time that an African court ever had annulled the results of a presidential race, and many saw it as a triumph of judicial independence.

But that ruling set off one of the most tumultuous periods in the country’s recent political history, leaving many Kenyans with little faith in their nation’s ability to conduct a fair election. Even the chairman of the electoral commission expressed doubts that he could manage a credible poll. Another election official fled the country after receiving death threats.

Just before the Supreme Court was due to rule Wednesday on the prospect of another delay, which theoretically would have allowed time for more electoral reforms, the deputy justice’s bodyguard was shot. Remarkably, not enough judges showed up to issue a decision.

Even before this election cycle, Kenyan electoral politics were somewhat fragile. In 2007, a disputed presidential vote devolved into ethnic violence that left more than 1,000 people dead.

This time, the dynamic is different, as Kenyatta now has total control over Kenya’s security forces. That makes protracted mob violence less likely but raises the specter of more police killings.

Perhaps even more damaging, many Kenyans are likely to see Kenyatta’s reelection as illegitimate, a major blow in a country that has struggled to build faith in its public institutions.

“Kenya is at risk of losing much of what it has gained since 2008 unless it comes together at this crucial moment to preserve its democracy and fundamental freedoms,” said a statement from 15 Western ambassadors and mission heads in Kenya, including the U.S. ambassador.

Violence Thursday was concentrated in opposition strongholds, particularly the western city of Kisumu, where three people were killed and 29 injured, according to the county governor.

In Mathare, a slum on the outskirts of Nairobi, witnesses said police charged into a crowd of protesters and started shooting live rounds. One man, Paul Oketch, 27, was shot in the head and killed.

“We tried to save him, but his pulse was already so weak when he arrived,” said Kennedy Odhiambo, a doctor’s assistant at Drugnet Medical Centre, a clinic in Mathare.

The rift in Mathare — and across much of the country — falls largely along ethnic lines, between Kenyatta’s Kikuyu tribe and Odinga’s Luo tribe. Although those tribes typically interact without issue, relations in Mathare were so strained Thursday that Luos remained on one side of the slum and Kikuyus on the other, with no one crossing an informal dividing line.

“Go ahead and kill us,” Odinga supporters yelled as they threw rocks at the police.

Meanwhile, Kenyatta supporters trickled to the polls to affirm their candidate’s reelection, seemingly a foregone conclusion.

“I am voting for a peaceful country, and I am voting for Uhuru,” said one Kenyatta supporter, Selly Bahati. “But it’s true that we are divided by tribe, and I don’t know what’s going to happen next.” She said her business selling shoes in Nairobi has declined by 50 percent during the past few months of political instability.

Bahati arrived at an empty polling center in Kibera, Nairobi’s largest slum. While she stood outside, one man yelled: “What are you doing there?”

By late afternoon, with word coming in that protesters had prevented voting materials from being distributed in some areas, the election commission made the announcement that the vote would be postponed until Saturday in four counties.

Kenyatta, however, told reporters as he voted in his home town of Gatunda that “90 percent of the country is calm, is peaceful.”

“What we have is a problem of tribalism, and tribalism is an issue that we must continue to deal with and fight with as we continue to develop our country,” he said. He pledged to unify the country if reelected.

A police statement backed up Kenyatta’s assertion, reporting violence in only five of the country’s 47 counties.

It remains unclear how Odinga’s supporters will respond once Kenyatta’s reelection is formally declared. Despite his talk of a “resistance movement,” Odinga has not explained how his position will change after decades as an opposition leader.

He called the probability of Kenyatta’s reelection a “coup d’etat” and the election a “day of infamy.” But in a statement Wednesday, he stopped short of encouraging violent protests.

That did not matter much to the protesters in Mathare, who continued their fight with police into the evening.

“We are not just fighting for Raila,” said Francis Mulecha, 26. “We are fighting for ourselves.”

Rael Ombuor contributed to this report.

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