UN human rights experts have expressed "legitimate concerns" about US juries failing to charge policemen involved in the deaths of two black civilians.
It is part of a broader "pattern of impunity" concerning minority victims, the UN said in a statement.
Thousands of people have taken to the streets in protest over the deaths of two black men at the hands of white officers in recent months.
Grand juries in Missouri and New York failed to charge either officer.
"I am concerned by the grand juries' decisions and the apparent conflicting evidence that exists relating to both incidents," UN Special Rapporteur on minority issues, Rita Izsak, said in a statement.
A trial process would ensure the evidence is considered in detail, she said.
"The decisions leave many with legitimate concerns relating to a pattern of impunity when the victims of excessive use of force come from African-American or other minority communities."
Watch: How the protests unfolded in a number of US cities
Human rights expert Mireille Fanon-Mendes-France, who currently heads the UN Working Group of Experts on People of African Descent, said the cases add to existing concerns.
She pointed to "longstanding prevalence of racial discrimination faced by African-Americans, particularly in relation to access to justice and discriminatory police practices".
The UN findings come amid ongoing protests over the death of Eric Garner, a black man held in an apparent chokehold by a white New York police officer.
