UN human rights experts have called on the United States and its leadership to "unequivocally and unconditionally" condemn racist speech and crimes, warning that a failure to do so could fuel further violent incidents.
The rare "early warning and urgent action" statement, which is reserved for serious situations, was issued by the UN Committee on the Elimination of Racial Discrimination.
It stopped short of criticising US President Donald Trump by name.
Mr Trump drew widespread condemnation when he blamed both sides for violence that broke out at a rally in Charlottesville, Virginia, organised by neo-Nazis and white nationalists.
One woman, Heather Heyer, was killed after a man linked to white nationalists drove his car into a crowd of counter-protesters.
CERD said it was "disturbed by the failure at the highest political level" of the US to reject racist demonstrations.
That failure, it said, could lead to "fuelling the proliferation of racist discourse and incidents" in the US.
The UN experts said the alleged perpetrators of the violence should be prosecuted and, if convicted, punished with sanctions commensurate with the gravity of the crime.
US officials should also "address the root causes of the proliferation of such racist manifestations, and thoroughly investigate the phenomenon of racial discrimination", the experts added.
They should ensure that freedom of expression, association and peaceful assembly "are not exercised with the aim of destroying or denying the rights and freedoms of others".
The US is among 177 countries to have ratified the UN pact against racial discrimination.
Over the past decade, the early warning has been issued in Burundi, Iraq, Ivory Coast, Kyrgyzstan and Nigeria.
Members of CERD are independent human rights experts drawn from around the world.
"We are alarmed by the racist demonstrations, with overtly racist slogans, chants and salutes by white nationalists, neo-Nazis, and the Ku Klux Klan, promoting white supremacy and inciting racial discrimination and hatred," said Anastasia Crickley, who chairs the UN panel.
Ms Crickley is the first Irish Chairperson of a UN Treaty Body and a founder member of the Migrants Rights Centre Ireland and of the National Traveller Women’s Forum, chairperson of Pavee Point Traveller and Roma Centre and of Community Work Ireland.
A former Head of Department of Applied Social Studies at Maynooth University, she has also previously worked as Chairperson of the European Union Monitoring Centre on Racism and of the EU Fundamental Rights Agency, as well as Personal Representative of the chair in office of the Organisation for Security and Cooperation in Europe.
