One ruling party official urged supporters "to castrate the enemy." Another called for drowning the regime's opponents in a lake.

Such hate speech spells trouble in Burundi, which is still reeling from President Pierre Nkurunziza's decision in 2015 to seek a disputed third term that provoked street protests and led to an estimated 1,200 deaths. Now Nkurunziza's government is pressing ahead with a May 17 referendum that could further extend his rule and usher in a new wave of bloodshed.

"We are shocked by such kinds of speech," said Gerard Hakizimana, president of a Burundian civic group known as Folucon-F. "All Burundians must live together in peace."

Burundians are being asked to vote yes or no to a proposal to extend the president's term from five years to seven, which would allow Nkurunziza to rule for another 14 years when his current term expires in 2020. His opponents are desperate to avoid that scenario, but they also seem powerless to stop him in the face of murderous threats.

Even before campaigning on the referendum officially started on May 1, tensions had been rising in this East African nation amid alleged detentions and killings of its perceived opponents. Human Rights Watch has noted "widespread impunity" for authorities and their allies, including the ruling party's youth wing, as they try to swing the vote in the president's favor. Two men recently died after beatings allegedly at the hands of state agents, the rights group said.

The violence is an "expression of fear" on the government's part and the "last recourse" for Nkurunziza, said Frederic Bamvuginyumvira, a former vice president who leads the opposition party Sahwanya-FRODEBU.

The United States last week denounced "violence, intimidation, and harassment" against those thought to oppose the referendum and expressed concern about the "non-transparent process" of changing the constitution. Burundi's Catholic bishops issued a statement expressing concern about the referendum's timing, citing "some problems in the democracy process" and urging unity.

Burundi's government strongly denies allegations it targets its own people, saying the charges are malicious propaganda spread by exiles. Last week it suspended BBC broadcasts in the country for six months, accusing it of spreading ideas that discredit the president. Voice of America broadcasts also were suspended.

The international community, however, has long expressed alarm over alleged abuses. International Criminal Court judges last year authorized an investigation into allegations of state-sponsored crimes in Burundi, a country that the U.N. human rights chief has called one of "the most prolific slaughterhouses of humans in recent times."

Concerns have risen in recent days. Last week Burundi's government arrested a party official who told a crowd he wanted the referendum's opponents thrown into Lake Tanganyika. Melchiade Nzopfabarushe, who once worked as a counselor in Nkurunziza's office, was swiftly convicted on charges of threatening state security and sent to prison for three years.

But rights activists were not impressed by the punishment, noting that many others who have made similar comments are still at large.

Members of the Imbonerakure, the ruling party's youth wing that has been accused by rights groups of perpetrating serious crimes on behalf of the government, have urged supporters in the past to harass opposition members, even to "impregnate" them.

"We have to castrate the enemy," Cyprien Sinzotuma, provincial secretary of the ruling party in rural Muyinga province, said during a recent march by Imbonerakure members. "It is total determination and we will fight up to the last."

SOS Medias Burundi, a network of independent journalists, has reported the arrests over a single week last month of more than 50 members of the opposition coalition Amizero y'Abarundi, whose leader Agathon Rwasa is the first vice president of the National Assembly. At least 10 of those were arrested while celebrating a colleague's successful defense of his university thesis, a meeting the authorities deemed subversive, the group said.

Late last month one human rights defender, Germain Rukuki, was sentenced to 32 years in prison on charges that included rebellion, a sentence Amnesty International called "an insult to justice." U.N. experts last year urged Rukuki's release, saying they were "concerned by the seemingly arbitrary detention."

Many in Burundi, a poor country that still relies heavily on foreign aid, worry that a new round of bloodshed will follow the referendum no matter its results. Already more than 400,000 people have fled the country since April 2015, according to the U.N.

Nkurunziza, a former rebel leader, rose to power in 2005 following the signing of the Arusha accords that ended Burundi's civil war that killed about 300,000 people. He was re-elected unopposed in 2010 after the opposition boycotted the vote. He said he was eligible for a third term in 2015 because lawmakers, not the general population, had chosen him for his first term. Critics called his pursuit of a third term unconstitutional.

"Nkurunziza is determined to capture the country's institutions and rule as an absolute monarch," activist group iBurundi said. "Of course this will not end well for him and for the country."

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Muhumuza reported from Kampala, Uganda.

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