The United States President on Sunday once again lambasted US pro American football players who refused to stand for the national anthem in protest against police brutality, stating that they should be fired or suspended.

  "If NFL fans refuse to go to games until players stop disrespecting our Flag & Country, you will see change take place fast. Fire or suspend!" Trump said on his Twitter account.

  "...NFL attendance and ratings are WAY DOWN. Boring games yes, but many stay away because they love our country. League should back U.S." the president said in another tweet.

  The controversy erupted last Friday when Trump at an Alabama rally criticized NFL players who have engaged in protests during the playing of the national anthem prior to their games.

  Last year, African American Colin Kaepernick - who, at the time, was playing for the San Francisco 49ers - attracted attention for not rising to his feet during the national anthem.

  Kaepernick that he was not going to stand during the playing of the anthem because he felt that the US oppresses blacks and other people of color.

  "Wouldn't you love to see one of these NFL owners, when somebody disrespects our flag, you'd say, 'Get that son of a bitch off the field right now. Out! He's fired,'" Trump said - to loud applause - at the rally in Huntsville, Alabama, and he has returned to the theme several times since then.

  Trump also got involved in another row on Saturday when he withdrew an invitation for Golden State Warriors NBA player Stephen Curry to visit the White House.

  Curry had admitted that he would vote against his team visiting the White House, as is traditional, to celebrate the NBA title they won last season, adding that his decision came in protest against the president.

  After Trump's broadside, the team confirmed that it will not visit the White House and said that it will use its visit to Washington next February to celebrate "equality, diversity and inclusion."

  Curry received messages of support from other NBA stars including Lebron James, with the Cleveland Cavaliers, the team that lost the final to Golden State last season.

  On his Twitter account, James called Trump a "bum" and blasted the president by saying "Going to White House was a great honor until you showed up!".

  Many NFL players on Sunday responded to Trump's comments by kneeling during the playing of the anthem, while many others who stood locked arms in a show of solidarity with those carrying out their peaceful protest.

  New England Patriots owner, Robert Kraft, who donated to Trump's presidential campaign, has issued a statement condemning the president's attack on players' right to protest, saying he was "deeply disappointed by the tone of the comments made by the President on Friday."