The UN chief's special adviser on genocide prevention has warned of a "high risk of crimes against humanity and of genocide" in the Central African Republic.
Adama Dieng and other UN officials briefed the Security Council on Wednesday on the continuing and unprecedented violence between Christians and Muslims in the country.
More than half the country's 4.6 million people need assistance, according to the UN, and nearly one million have fled their homes after mostly Muslim Seleka rebels seized power in a March coup d'etat that ousted former President Francois Bozize.
Christian self-defence groups known as "anti-balaka" (anti-machete) have taken up arms against them, and the UN estimates that retaliatory violence has claimed thousands of lives.
The officials spoke of children being beheaded, entire villages burned and a complete breakdown of law and order, and they urged the deployment of more peacekeepers as soon as possible.
"The level of hatred between these communities shocked me," Dieng said, listing widespread reports of summary executions, mutilation and sexual violence among the "widespread and massive" human rights violations.
Restoring peace will be difficult "without addressing the current culture of impunity," he added.
Dieng and the other officials spoke after a visit last month as violence spiralled.
Despite the dark outlook for the country, they expressed hope at this week's election of Catherine Samba-Panza as interim president, and at the $496m in humanitarian assistance newly pledged by international donors.
They also welcomed the approval by European Union foreign ministers this week of a potential joint military force of about 500 troops to assist the roughly 1,600 French troops and about 4,600 African troops trying to restore order.
Samba-Panza pledged after her election to hold talks with armed groups.
"I want to meet with the armed groups and listen to them," she told reporters. "If they took up arms, then there is a reason for that."
The statements came as the Red Cross said it had found 11 corpses, most burnt beyond recognition, dumped in the capital Bangui.
Antoine Mbao Bogo, president of the Central African Red Cross Society, said nine of 11 bodies collected from Bangui's mostly Muslim northern neighbourhood of PK11 earlier this week had been set alight.
He added that the Red Cross had collected 87 bodies in the past five days across the country.