The United Nations and Washington have warned separately against possible violence as Burundi appears poised to become the latest African country to extend presidential term limits.
“Everyone will suffer if Burundi explodes into violence during or after the referendum,” the UN human rights spokesman Rupert Colville said Tuesday.
At the same time, a US State Department official criticised efforts by incumbents to extend term limits saying it impedes democratic development.
Burundians are scheduled vote on Thursday in a constitutional amendment that could enable President Pierre Nkurunziza to remain in power until 2034.
If the voters approve the proposed amendments, Mr Nkurunziza will join the ranks of 13 African presidents who have rolled back term limits in recent years.
Burundi's ruling party favours the changes to the constitution that would lengthen presidential terms to seven years from five and allow Mr Nkurunziza to stand for re-election in 2020 and again in 2027.
The 54-year-old evangelical Christian came to power in 2005 after a peace agreement signed in Arusha in 2000 that ended a civil war in which an estimated 300,000 people were killed.
Mr Nkurunziza returned to office in 2010, with opposition parties boycotting a vote they said was rigged.
Violence ensued in 2015 when the president declared himself eligible for another term, despite a stipulation in the Arusha Accord that an incumbent head of state can be re-elected only once.
Burundi has remained volatile for the past three years, during which an estimated 1,200 people have been killed by government forces or unidentified groups.
UN human rights spokesman Colville spoke on Tuesday of a “febrile atmosphere” in Burundi as the “extremely controversial and divisive referendum” nears.
Last week, some 26 people were killed in a village in northwest Cibitoke province by an unknown armed group.
No one claimed responsibility for the atrocity, which the government attributed to an unnamed “terrorist group” from neighbouring Democratic Republic of Congo.
Mr Colville termed the attack as a “dangerous development.”
“Tensions are rising sharply in the wake of this attack, with many dreading what may happen during and after Thursday’s referendum,” Mr Colville added.
Leading opponents of the proposed constitutional changes have been subjected to arbitrary arrests by security forces, Mr Colville said.
The US has denounced such intimidation and has called on the Burundian authorities to respect freedom of expression, which the State Department terms “an essential component of a credible referendum.”