The Africa Union has pledged not to allow a "genocide" to take place in Burundi, while a UN human rights assembly has approved a resolution calling for the immediate deployment of experts there to investigate abuses and rein in violence.
At least 87 people were killed last week in the African nation in the worst violence in months linked to President Pierre Nkurunziza's disputed third term.
The 47-member Human Rights Council approved by consensus on Thursday in Geneva, Switzerland, a text that calls for the UN human rights chief to send in a mission of experts who are to report regularly on the rights situation in Burundi.
In its decision, the UN body condemned serious human rights abuses committed by security forces, government supporters and the opposition.
Its members also expressed concerns about the government's violent crackdown on civil society.
Earlier on Thursday, the UN high commissioner for human rights said Burundi was "on the very cusp of civil war" and called for the involvement of the International Criminal Court.
Zeid Ra'ad Al Hussein said: "Those responsible for human rights violations and instigating violence should be subject to sanctions, including asset-freezes and travel bans.
"The situation needs urgent, concerted, decisive attention from the international community."
At least 400 people have been killed since protests against Nkurunziza's third presidential term started in April, and nearly 3,500 have been arrested in the political crisis, according to UN figures.
At least 220,000 people have fled the country.
The warning of a risk of looming ethnic bloodshed came as the 54-member African Union said the continent "will not allow another genocide to take place on its soil", a reference to the horror in Rwanda in 1994.
READ MORE: Bodies on the streets as violence rocks Burundi
Al Jazeera's Mohammed Adow, reporting from the capital Bujumbura, said the plans for the deployment of UN peacekeepers had been "outrightly rejected" by Burundi's government.
"A government spokesman said those who are agitating for the deployment of foreign peacekeepers in Burundi have ulterior motives," he said.
The special session at the UN's top rights body was debating a draft resolution tabled by the US pressing for Hussein to urgently dispatch an investigative team to Burundi, with Keith Harper, the US ambassador, decrying "a climate of fear" in the country.
"The international community must use all of the tools available to push for an immediate end to the cycle of violence perpetrated by both the security forces and elements of the armed opposition." Harper said.
Separately, Adama Dieng, a UN adviser for the prevention of genocide, said that both the government and the opposition were manipulating ethnic tensions in Burundi, pitting Hutus and Tutsis against each other.
"The country appears to be on the verge of a descent into violence that could escalate into atrocity crimes," he told the council.
He voiced alarm that hate speech and rhetoric is currently being used in Burundi that resembles that seen before the 1994 genocide in neighbouring Rwanda.
The surge in violence has raised fears of a return to civil war, a decade after the end of a 1993-2006 conflict between rebels from the Hutu majority and an army dominated by minority Tutsis, which left 300,000 people dead.
Ban Ki-moon, the UN secretary-general, gave warning earlier this week that Burundi was on "the brink of a civil war that risks engulfing the entire region".
Source: Al Jazeera and agencies