As he prepared to board Air Force One to return to Washington from New Jersey, Mr Trump said the players protesting the anthem were "very disrespectful to our country" and called again on owners to stop what he considers unpatriotic displays in America's most popular sport.

"This has nothing to do with race," Mr Trump said. "This has to do with respect for our country."

The president's attack on athletes turned the anthems - usually sung during commercials - into must-watch television. In some NFL stadiums, crowds booed or yelled at players to stand. There was also some applause.

The NFL and its players, often at odds, used Sunday's anthems to show unity. One of Trump's biggest supporters in the NFL, Patriots owner Robert Kraft, joined the chorus when he expressed "deep disappointment" with Mr Trump.

"I like Bob very much. He's my friend. He gave me a Super Bowl ring a month ago. So he's a good friend of mine and I want him to do what he wants to do," Mr Trump said. "... We have great people representing our country, especially our soldiers our first responders and they should be treated with respect. And when you get on your knee and you don't respect the American flag or the anthem."

The protests started more than a year ago when former San Francisco 49ers quarterback Colin Kaepernick refused to stand during the anthem as a protest of police treatment of minorities. This season, no team has signed him, and some supporters believe NFL owners are avoiding him because of the controversy.

Defensive star Von Miller was among the large group of Denver Broncos who took a knee in Buffalo on Sunday, where Bills running back LeSean McCoy stretched during the anthem.

"We felt like President Trump's speech was an assault on our most cherished right, freedom of speech," said Miller, who normally steers clear of politics and social issues.

Dozens of more players protested before the Raiders-Redskins game, the final one of the day and not far from the White House in Landover, Maryland. All but a handful of Raiders sat on their bench and seven Redskins took a knee while their teammates stood arm-in-arm along with owner Dan Snyder and president Bruce Allen.

In Chicago, the Pittsburgh Steelers stayed in the tunnel except for one player, Army veteran Alejandro Villanueva, who stood outside with a hand over his heart. Both the Seahawks and Titans stayed inside until after the national anthem was over in Nashville, a throwback to the pre-2009 NFL when teams, not the league, set pre-game policy regarding players standing on the sideline for the anthem.

A handful of NFL players had been continuing Kaepernick's protest this season, but that ballooned following Mr Trump's two-day weekend rant. It began with the president calling for NFL protesters to be fired and continued on Saturday when he rescinded a White House invitation for the NBA champion Golden State Warriors over star Stephen Curry's criticism.

Super Bowl MVP Tom Brady was among the New England Patriots who locked arms in solidarity in Foxborough, Massachusetts. Aaron Rodgers did the same with his teammates in Green Bay.

"Standing with locked arms is good, kneeling is not acceptable. Bad ratings!" Mr Trump tweeted on Sunday.

The issue reverberated across the Atlantic, where about two dozen players from the Jacksonville Jaguars and the Baltimore Ravens took a knee during the playing of the US anthem at Wembley.

"We stand with our brothers," Ravens linebacker Terrell Suggs said. "They have the right and we knelt with them today. To protest, non-violent protest, is as American as it gets, so we knelt with them today to let them know that we're a unified front."

Jaguars owner Shad Khan and players on both teams who were not kneeling remained locked arm-in-arm throughout the playing of the anthem and God Save The Queen.

AP