Burundi's authorities have dismissed a BBC investigation into alleged secret torture sites as "fake news".
The BBC Africa Eye report said the government was running secret detention houses to silence dissent.
It showed footage, widely shared on social media, of blood flowing from the drain of a house in the capital.
Prosecutor General Nyandwi Sylvestre maintained that the blood came from goats slaughtered to mark the Muslim festival of Eid.
Since independence in 1962, Burundi has been plagued by ethnic tension.
Hundreds of people have died since unrest began in 2015, amid protests over President Pierre Nkurunziza's third-term bid and a subsequent failed coup, with thousands fleeing the country.
The Africa Eye team spoke to former intelligence officials, as well as detainees, who said that they either heard or saw victims being tortured with electric cables or being killed.
A man named in the report as "Nathan" said he worked as a guard for Burundian intelligence chief Alexis Ndayikengurukiye - also known as "Nkoroka".
Nathan said he was at the house where blood was seen flowing from the gutter when Nkoroka ordered three detainees to be beheaded.
He witnessed two of them being beheaded, a third man was killed after he tried to escape.
Burundi's prosecutor general told reporters in the capital, Bujumbura, that since November 2015 when an arms cache was discovered at the house in question, the property had been guarded by police and not by intelligence officers.
Mr Sylvestre said that the BBC report failed to provide any evidence of secret prisons in Burundi.
At least 21 other torture locations in Burundi have been reported by victims and intelligence agents to the UN, the Burundian civil society organisation Ndondeza, and to the BBC.
The Burundian government has always denied carrying out any human rights violations.
In 2015, armed police are alleged to have killed hundreds of protesters demonstrating against President Nkurunziza's decision to run for a third term in office, saying he was violating the constitution.
Mr Nkurunziza subsequently won the election that year - and has since promised to stand down in 2020.