Lee- who refused to identify Trump by name - called Charlottesville an "ugly, ugly, ugly blemish on America", and condemned the president for not using it as an opportunity to denounce the Ku Klux Klan and the alt-right.
"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".
His new film BlacKkKlansman premiered at Cannes on Monday night to a rousing standing ovation.
Based on Ron Stallworth's 2014 book Black Klansman, it presents the kind of scenario that you just couldn't make up, following Stallworth (Denzel's son John David Washington), the first African-American cop in the Colorado Springs police force, as he goes undercover to infiltrate the local chapter of the Ku Klux Klan. Topher Grace portrays former KKK leader David Duke.
After Lee finished production on "BlacKkKlansman", he added an ending with actual footage from Charlottesville and Trump's televised response.
The film ends with footage from the protests in Charlottesville, where a woman was killed after a man plowed his auto into a crowd of counter-protesters during the "Unite the Right" rally.
Lee criticized Trump's response to a white nationalist rally Charlottesville, Va. last summer, and reportedly referred to the president as a "mother--".
"I know my heart, I don't care what the critics say or anybody else, but we are on the right side of history with this film".
Lee said he reached out to Heyer's mother, Susan Bro, and received her permission to include footage of her daughter being run down by a white supremacist in a auto.
"I was not going to put that murder scene in the film without her blessing", said Mr Lee.
'Produced by the team behind the Academy-Award® winning Get Out, BlacKkKlansman offers an unflinching, true-life examination of race relations in 1970s America that is just as bracingly relevant in today's tumultuous world'. It's all over the world. We can't be silent. "It's not a Black, white, or brown [problem], it's everybody", he said. Lee has frequently debuted films at Cannes, including Do the Right Thing in 1989.
During the BlacKkKlansman press conference, Lee also discussed the rise of Right-wing nationalism and called on all people to speak up. "This is not just something that pertains to the United States of America, this bulls- has gone over the world".
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