US Attorney General Jeff Sessions denounced a deadly car ramming incident in Virginia on Saturday when white nationalist activists and counter-protesters clashed, after President Donald Trump came under sharp criticism for his own tepid response.

Sessions, the top law enforcement official in the country, said "the violence and deaths in Charlottesville strike at the heart of American law and justice."

"When such actions arise from racial bigotry and hatred, they betray our core values and cannot be tolerated," Sessions added.

Federal investigators have opened a probe into the incident.