NFL boss Roger Goodell has admitted the league made mistakes in not listening to players who spoke out against racism as the 'Black Lives Matter' movement continues to gain momentum.

The National Football League's commissioner made the admission in a video shared on Friday denouncing racism in the United States amid widespread protests over police brutality against black people.

Goodell said in the video: "We, the National Football League, admit we were wrong for not listening to NFL players earlier and encourage all to speak out and peacefully protest.

"We, the National Football League, believe black lives matter."

The NFL has been locked in an ongoing debate with players over kneeling protests during the customary pre-game playing of the national anthem.

NFL Commissioner Roger Goodell encouraged people to peacefully protest against racism

The practice was popularised in 2016 by quarterback Colin Kaepernick, who is black, as a way to protest against racial injustice and police brutality.

Kaepernick, who in 2013 led the San Francisco 49ers to the Super Bowl but lost to the Baltimore Ravens, filed a grievance against the league in 2017, claiming collusion as no teams signed him after he parted ways with the Niners.

The NFL and Kaepernick settled in 2019, but he has not played in the league since 2016.

While Goodell did not directly apologise to Kaepernick in the video for 'taking a knee', the commissioner's admission opens up a debate about whether the quarterback was wrongfully ousted out of the game.

"Without black players, there would be no National Football League," said Goodell.

"Protests around the country are emblematic of the centuries of silence, inequality and oppression of black players, coaches, fans and staff.

"I will be reaching out to players who have raised their voices and others on how we can improve."

The NFL sent the video out just hours after US President Donald Trump renewed his call for an end to kneeling protests during the national anthem.

"We should be standing up straight and tall, ideally with a salute, or a hand on heart," Trump wrote on Twitter. "There are other things you can protest, but not our Great American Flag - NO KNEELING!"

The statement was a response to quarterback Drew Brees, who apologised this week for equating the kneeling protest with disrespecting the American flag.

On Thursday, several players, including reigning Super Bowl MVP Patrick Mahomes of the Kansas City Chiefs, appeared in a video on social media calling for the league to "admit wrong in silencing" players, and to support protests.

"How many times do we need to ask you to listen to your players?" Chiefs player Tyrann Mathieu said in the video.

Colin Kaepernick (centre) popularised 'taking a knee' during the US national anthem as a way of protesting against racism

The league also faced criticism earlier this year when just one of five head-coaching vacancies went to a non-white candidate in the most recent hiring cycle.

Last month the NFL introduced rules designed to boost racial diversity among coaching staffs.