Tens of thousands of people are attending a controversial rally in Washington DC organised by conservative talk show host Glenn Beck.
Civil rights leaders criticised Mr Beck for holding the rally at the Lincoln Memorial, the place where Martin Luther King Jr made his "I Have a Dream" speech 47 years ago to the day.
Mr Beck, a presenter for Fox News, insisted the timing was a coincidence.
A counter-rally called by civil rights campaigners is also under way.
Addressing the crowd, Mr Beck said the US had "wandered in darkness" for too long.
"America today begins to turn back to God," he said.
He told the crowd the timing of the "Restoring Honour" rally was coincidence but also divine providence.
Former US vice-presidential hopeful Sarah Palin also spoke at the rally.
A counter-rally organised by the civil rights leader Rev Al Sharpton is taking place at the same time.
Participants are marching to the site of a proposed memorial to Dr King, not far from the Lincoln Memorial.
Civil rights leaders say Mr Beck's message runs counter to that of Dr King.
"It's an affront to what the civil rights movement stood for," Georgia Congressman John Lewis, who spoke at the 1963 March on Washington, told the Atlanta Journal-Constitution.
"We didn't do anything in anger and never tried to divide people. Glenn Beck is a very divisive force."
The 1963 march was a pivotal moment in the US civil rights movement. Dr King's "I Have a Dream" speech at the Lincoln Memorial that day foresaw a united nation, free from racial discrimination. It is one of the most celebrated works of American oratory.
Glenn Beck says he was unaware of the coincidence in dates
Mr Beck is a prominent voice in the anti-establishment Tea Party movement. Last year he accused President Barack Obama of racism, saying he had a "deep-seated hatred for white people or the white culture".
He said when he was planning the rally in the US capital he was unaware that Saturday 28 August would be the anniversary of the 1963 march.
"It's not the date, it's the message," he said on his television show on Thursday.
"I've heard it over and over again in the media that because of this event, on the date of this event, I'm somehow or another hijacking Dr Martin Luther King's speech. I'm not big enough to do that. No-one is."
The Tea Party movement has galvanised conservatives opposed to taxes and government intervention.