Obama speaks on King anniversary
US president Barack Obama has held himself up as a symbol of the change envisioned by Martin Luther King 50 years ago during a speech in Washington.
The first black US president was speaking on the steps of the Lincoln Memorial where Dr King delivered his I Have A Dream speech in the March on Washington on August 28, 1963.
But he also pointed to America's lingering economic disparities as evidence that King's hopes remain unfulfilled.
Speaking earlier at the celebration TV presenter Oprah Winfrey said King forced the US to "wake up, look at itself and eventually change", adding that the civil rights leader's lessons continue to inspire people all over the world.
Ms Winfrey said Dr King recognised that Americans shared the same dreams and that their hopes were not different based on race. She said Dr King was right when he said all Americans' destinies are intertwined and would rise or fall based on how people treat their neighbours.
Ms Winfrey said she asked her mother as a nine-year-old girl why her family was not there for the march. Ms Winfrey said it took 50 years, but she finally arrived on the steps of the Lincoln Memorial to mark the anniversary of King's march.
Former US president Bill Clinton said the anniversary marks "one of the most important days in American history".
Mr Clinton said that march, and that speech, "changed America... opened minds and melted hearts ... and moved millions".
Mr Clinton added that racial inequalities remain but he said it is time to stop complaining and instead get to work - for better education opportunities for all children and implementing health care for all.
He said "we must push open those stubborn gates" that are holding America back.