Hollywood legend Robert Redford has called on US leaders to apologise for the war in Iraq.
Redford's Sundance Institute supports the festival
The actor was speaking at the start of the Sundance Film Festival in Utah, where the opening movie recalled protests over the Vietnam war in 1968.
Redford said he, like many others, had shown a "spirit of unity" with the US government after 11 September 2001.
"We put all our concerns on hold to let the leaders lead," he said. "I think we're owed a big, massive apology."
The actor, whose Sundance Institute for independent film runs the annual festival, usually steers clear of political messages in his opening speech.
Festival opener Chicago 10 recounts the demonstrations surrounding 1968's Democratic National Convention, which saw protestors clash with the National Guard.
Using a cutting-edge blend of historical footage and animation, director Brett Morgen's film examines the trial of the famed "Chicago Seven," who were convicted of inciting riots.
Protestors clashed with Chicago police and the National Guard
Morgen, who took the stage to a standing ovation after the screening, said one of his goals in making the film was to "mobilise the youth in the country to get out and stop this war".
His film is one of many referencing the Iraq conflict at this year's Sundance festival.
Ghosts of Abu Ghraib deals with the abuses that occurred in an Iraqi prison in 2003, while No End In Sight is an examination of the Bush administration's conduct in the country.
The programme for the festival has attracted controversy with the inclusion of films that include shocking sexual content.
A documentary called Zoo deals with the practice of bestiality.
And the dark drama Hounddog portrays the rape of a young girl, played by 12-year-old actress Dakota Fanning.
"Those are issues that are on the table, whether you want to face them or not," said Redford.
"If you don't expose these things, if you don't put the light on them, then they could get worse."
But the event also features many films with a more uplifting feel.
The Good Life, from writer and director Steve Berra, tells of a young man running an old cinema in a small town.
Padre Nuestro is about a young man who meets up with a group of illegal immigrants heading from Mexico to New York after he chooses to flee his criminal past.
More than 120 films will be screened throughout the 10-day festival, which ends on 28 January.