Burundians vote Thursday in a referendum that could keep the president in power for another 16 years and threatens to prolong a political crisis that has seen more than 1,000 people killed and hundreds of thousands fleeing to neighboring countries.

Many in this East African nation do not see a positive outcome no matter the results of the vote, which President Pierre Nkurunziza's government forced through despite widespread opposition and the concerns of the United States and others warning of continued bloodshed. The country descended into crisis in 2015 when Nkurunziza pursued a disputed third term.

Now Burundi's 5 million voters are asked to approve a change to the constitution that would extend the length of the president's term from five years to seven and would allow him to stand for two more terms. Nkurunziza has forcefully urged voters to support the referendum.

"Whoever opposes this election will meet God's power," the president warned earlier this month while campaigning.

Tensions are even higher after unidentified attackers armed with machetes and guns carried out a massacre Friday in the rural northwest near Congo, killing 26 people, many of them children. The government blamed a "terrorist group."

While it is not clear whether the attack was linked to Thursday's referendum, it was "a very dangerous development," United Nations human rights chief Zeid Ra'ad al Hussein said Tuesday.

Zeid, who has called Burundi one of "the most prolific slaughterhouses of humans in recent times," warned that "everyone will suffer" if Burundi explodes into violence during or after the vote.

Some in Burundi's opposition, which has faced hate speech from officials including threats of drowning and castration, say they have little choice but to fight back. Boycotting the vote is risky following a presidential decree that criminalized calls to abstain from casting a ballot.

"The only available option now is to use guns and we are determined to use all means to realize our cause," said Hussein Radjabu, who was a Nkurunziza ally before being jailed on treason-related charges. He later escaped from prison and fled the country.

The referendum is rigged in Nkurunziza's favor, Radjabu told The Associated Press by phone.

Burundi's government strongly denies allegations it targets its own people, saying the charges are malicious propaganda spread by exiles.

The international community, however, has long expressed alarm. An estimated 1,200 people have been killed since early 2015, and International Criminal Court judges last year authorized an investigation into allegations of state-sponsored crimes.

As Thursday's referendum approached, Human Rights Watch noted "widespread impunity" for authorities as they tried to swing the vote in the president's favor, citing two recent deaths after beatings allegedly at the hands of state agents.

Opposition leaders call Nkurunziza, declared in March by the ruling party as "supreme guide of all times," a dictator unwilling to leave office.

"President Nkurunziza had declared that he would leave in 2020," Agathon Rwasa, chairman of the Amizero y'Abarundi opposition coalition, told a rally on Monday. "Now he wants to remain in power arguing that he was sent by God" while both the economy and diplomatic relations decline.

Impoverished Burundi has been volatile since the 1990s, riven especially by ethnic discord in the military as Hutu and Tutsi officers jockey for power.

The 54-year-old Nkurunziza, a former rebel leader who is the son of a Hutu father and a Tutsi mother, rose to power in 2005 following the peace deal ending a civil war in which some 300,000 people died. A born-again Christian who won some support with public displays of faith, he was re-elected unopposed in 2010 after the opposition boycotted the vote.

Protests erupted in April 2015 after Nkurunziza said he was eligible for a third term because lawmakers, not the general population, had chosen him for his first term. Critics called a third term unconstitutional, as the deal ending the civil war says the president can be re-elected only once.

Amid the protests, a group of senior armed forces officers attempted a coup. While peace talks between the government and the opposition stalled, Nkurunziza tightened his grip on the army, allegedly by purging officers deemed disloyal, according to the International Federation of Human Rights and local civic groups.

In the streets of the capital, Bujumbura, where the police have increased their presence this week, people say they are worried about what comes next.

One man told the AP he will vote for changing the constitution even though he opposes it because he fears there will be secret cameras spying on people in the voting booth.

"So I will go to vote for 'yes' in order to save my job," the public transport operator said, speaking on condition of anonymity for safety reasons.

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Muhumuza reported from Kampala, Uganda. Associated Press writer Ignatius Ssuuna in Kigali, Rwanda contributed.

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