The US President was under increasing pressure to address the violence in Charlottesville, with politicians from both sides criticising his failure to condemn far-right organisations.
At a news conference at the White House on Monday, Mr Trump said: “Those who spread violence in the name of bigotry strike at the very core of America.
“Racism is evil. And those who cause violence in its name are criminals and thugs, including the KKK, neo-Nazis, white supremacists and other hate groups that are repugnant to everything we hold dear as Americans.”
Mr Trump said anyone found to have acted criminally would be held “fully accountable”, adding that: “No matter the colour of our skin we all live under the same laws, we all salute the same great flag, and we are all made by the same almighty God.”
At the weekend, Mr Trump had claimed “many sides” were involved in the violence, but stopped short of condemning white supremacists.
The US President has been at his New Jersey golf club on a “working vacation”, but returned to Washington on Monday to sign an executive action on China’s trade policies.
Richard Spencer, president of white nationalist think tank the National Policy Institute, dismissed Mr Trump’s condemnation.
He told Sky News: “It has a lot of kumbaya and a lot of nostalgia to it, ‘we need to rediscover these bonds we’ve had together’, does anyone really believe that?
“I do think there was an American nation that did act as one, that had fewer divisions, that emerged probably by the time of the Great War.
“No one identifies as a white supremacist or anything like that. I’m not the KKK, I don’t engage in violence and I don’t want to rule over other races.
“It’s very easy to say things like ‘racism is evil’. Everyone throughout world history had a sense of who they were, they had a sense of maintaining their community and their family and their nation and their civilisation etc.
“It’s very silly to say things like that and I just can’t take it seriously.”
Now that Ken Frazier of Merck Pharma has resigned from President’s Manufacturing Council,he will have more time to LOWER RIPOFF DRUG PRICES!
— Donald J. Trump (@realDonaldTrump) August 14, 2017
On Monday, attorney general Jeff Sessions said the death of paralegal Heather Heyer, 32, who was killed when a car ploughed into a group of counter-protesters in Charlottesville, “does meet the definition of domestic terrorism in our statute”.
He told ABC: “You can be sure we will charge and advance the investigation towards the most serious charges that can be brought, because this is an unequivocally unacceptable and evil attack that cannot be accepted in America.”
The man arrested over Ms Heyer’s death – 20-year-old James Fields – appeared in court on Monday on a second-degree murder charge. He was held without bail.
It comes as Merck chief executive Kenneth Frazier – one of America’s most prominent black executives – quit the US President’s American Manufacturing Council over Mr Trump’s response to the violence.
In a tweet announcing his resignation, Mr Frazier said: “America’s leaders must honour our fundamental views by clearly rejecting expressions of hatred, bigotry and group supremacy, which run counter to the American ideal that all people are created equal.”
The US President hit back, saying that now that “Ken Frazier of Merck Pharma has resigned from the President’s Manufacturing Council, he will have more time to LOWER RIPOFF DRUG PRICES!”
Several executives from top US companies have stepped down from a number of presidential advisory councils in protest over Mr Trump’s policies.
Tesla chief executive Elon Musk and Walt Disney chief executive Robert Iger quit the Strategic and Policy Forum in June after Mr Trump announced the US would withdraw from the Paris climate accord.
Mr Musk has also left the manufacturing council.
Former Uber chief executive Travis Kalanick left the President’s business advisory council in February amid pressure from his company over the Trump administration’s immigration policies.