In one of the last acts of his eight-year presidency, President Barack Obama has given out the Presidential Medal of Freedom to 20 citizens, as a reward for their contribution to the US.

The Medal of Freedom is America's highest honour for a civilian, and rewards contributions towards security or national interests, as well as cultural or other significant contributions.

Last year, Steven Spielberg and Barbra Streisand were among those to receive the honour.

President Obama said in a statement: "The Presidential Medal of Freedom is not just our nation's highest civilian honor - it's a tribute to the idea that all of us, no matter where we come from, have the opportunity to change this country for the better.

"From scientists, philanthropists, and public servants to activists, athletes, and artists, these 21 individuals have helped push America forward, inspiring millions of people around the world along the way."

Among those receiving the medal were actor Robert De Niro, comedienne and chat show host Ellen DeGeneres, Tom Hanks, and philanthropists Bill and Melinda Gates.

In the sporting world, NBA star Kareem Abdul-Jabbar and NBA six-time champion Michael Jordan both received the medal.

Bruce Springsteen and Diana Ross also received the award for their contribution to culture.

In the scientific community, mathematician and computer scientist Margaret Hamilton, and physicist Richard Garwin were both given the award.

Rear Admiral Grace Hopper, known as "Amazing Grace", was given the award posthumously for her programming and computer science work, along with Elouise Cobell, who was awarded posthumously for her work fighting for Native American communities.

DeGeneres tweeted before the ceremony that she wasn't allowed into the White House because she forgot her ID, posting a forlorn photo of her sitting on a bench outside.

She also posted a 'Mannequin Challenge' video in which all the recipients of the award stood as if frozen in time.

DeGeneres was so humbled by the statement read out as she was given the award that she was brought to tears.

The speech cited her involvement in LGBT equality and rights, and her championing of equal marriage.

"Her courage and candour helped changed the minds of millions of Americans, accelerating our nation's constant drive towards equality and acceptance for all.

"Again and again, she has shown us that a single individual can help make the world a more fun, more open, more loving place, so long as we just keep swimming."

Full list of Presidential Medal of Freedom recipients: