United States president Donald Trump has urged National Football League fans to stop going to games "until players stop disrespecting our flag and country".

Over the weekend, the 71-year-old has denounced the kneeling protests undertaken by some NFL players during the national anthem and rescinded a White House invitation for NBA champion Stephen Curry.

Trump tweeted on Sunday: "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!

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

Trump's statements have brought swift condemnation from league executives, star players and miscellaneous celebrities alike.

On Saturday, the kneeling protests spread to avenues beyond American football, with musician Stevie Wonder and baseball player Bruce Maxwell joining in.