More crimes against humanity were committed in Burundi in 2017 and 2018, whipped up by rhetoric from top officials including President Pierre Nkurunziza, a U.N. human rights report said on Wednesday.
Burundian officials said the report was "lies".
Burundi has tried and failed to stop the U.N. Commission of Inquiry on Burundi, set up by the U.N. Human Rights Council in 2016, and refuses to cooperate with it. The commission said last year that officials at the highest level were responsible for crimes against humanity.
The Commission's latest report said there were reasonable grounds to believe crimes against humanity were continuing, including murder, torture and rape.
Nkurunziza's spokesman Jean Claude Karerwa said it was sad to see human rights bodies becoming the political instruments of Western powers. He called commission chairman Doudou Diène a liar who should apologise to Nkurunziza and Burundi's people.
"If he is really a human rights defender, he has to constantly bear in his mind that the people he is tarnishing and blackmailing are human beings like him," Karerwa said.
Burundi's Human Rights Minister Martin Nivyabandi said the report was misleading and insulting.
Burundi has been seized by violence since early 2015 when Nkurunziza said he would seek a third term, widely seen as a breach of the constitution.
Clashes between security forces and rebels left hundreds dead and forced about half a million to flee -- rattling a region still haunted by the memories of the 1994 genocide in neighbouring Rwanda, which has a similar ethnic mix to Burundi.
In May a referendum changed the constitution in a way that could allow him to remain president until 2034.
Diène told reporters that heightened scrutiny was crucial as human rights abuses were likely to increase as the 2020 election approached.
Commissioner Françoise Hampson said that after Burundi's departure from the International Criminal Court last year, the commission was the only independent international body documenting human rights abuses.
Burundi's security was directed by a "committee of generals" around Nkurunziza, said the commission, which has drafted a secret list of human rights violators.
Members of the National Intelligence Service and the police, including high-ranking officials, committed a large number of human rights violations, and the Imbonerakure, the youth wing of the ruling party, was playing a growing role, the report said.
Opponents of the government had been detained and tortured, often by the Imbonerakure, the commission said.
The number of summary executions appeared to have diminished since 2015, when they took place on a large scale, but the perpetrators took care to cover their tracks by weighing down the bodies and throwing them into rivers, it said.
"There are more people who are disappearing than were disappearing before. We don't know if they are ending up dead. There's every reason to believe that in a large number of cases they are," Hampson said.