An unknown armed gang killed at least 23 people on Friday night in an attack on a village in northwest Burundi, a local official said."We have already counted 23 people killed, including men, women and children, but the toll could increase as we continue to search for victims," the official told AFP on condition of anonymity.Witnesses described an hours-long orgy of violence and said a further 10 people were wounded by a group armed with guns and knives who also set fire to buildings in a village in the Cibitoke province bordering the Democratic Republic of Congo and Rwanda."These criminals went house to house and committed real carnage," said the official, saying he was "horrified" by the violence."Some of the victims were stabbed, others were shot, there is even a whole family that was burned alive in their home."The perpetrators and their motive are not yet known, but local residents said the attackers crossed into DRC after carrying out the raid at around 22:00 on Friday night."For now, these criminals have not been identified, but an investigation is underway to determine their identity," said a police officer, who did not want to be named.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and FacebookThe attack comes as tensions rise days ahead of a constitutional referendum on May 17 which could allow President Pierre Nkurunziza to stay in power until 2034.The 54-year-old president has ruled the tiny central African nation since 2005. His run for a controversial third term in 2015 triggered a deep political crisis that has since seen 1 200 people killed and 400 000 flee their homes.The violence and abuses are being investigated by International Criminal Court (ICC) while a vicious press crackdown has seen the majority of independent journalists leave the country.In a report last month Human Rights Watch accused Burundi's government of killing, beating and intimidating suspected opponents of the referendum in a bid to ensure Nkurunziza's victory in the referendum.The government has in recent weeks deployed soldiers to the border areas after accusing exiled opposition groups of seeking to disrupt the vote.The vote is taking place in tightly-controlled conditions, and parties which advise electors to abstain - rather than cast a Yes or No ballot - risk up to three years' jail.Earlier this month Burundi's press regulator suspended broadcasts by the BBC and Voice of America (VOA) and warned other radio stations, including Radio France International (RFI), against spreading "tendentious and misleading" information.