Houston Texans players kneel and stand during the singing of the national anthem before an NFL football game against the Seattle Seahawks, in Seattle. Picture: AP Photo/Elaine Thompson, File

Washington - US football players who refuse to stand for the national anthem maybe "shouldn't be in the country," President Donald Trump said on Thursday.

He welcomed a new National Football League owners' rule that players must stand during the Star Spangled Banner at games, unless they stay in the locker room.

"Well I think that's good. I don't think people should be staying in locker rooms," Trump told the "Fox & Friends" TV show, which is one of his favorites.

"You have to stand proudly for the national anthem or you shouldn't be playing. You shouldn't be there. Maybe you shouldn't be in the country."

Trump said "the NFL owners did the right thing if that's what they have done."

Last year Trump described players who kneeled during the anthem to draw attention to racial injustice as "sons of bitches" who were insulting the flag and the nation.

The remarks prompted a wave of kneeling protests across the league in September, angering some fans and placing several conservative, Trump-supporting team owners in an awkward position as NFL television ratings dropped.

Trump declined to take credit for the change in NFL policy, telling "Fox & Friends" that although he raised the issue "I think the people pushed it forward."

Under current NFL regulations, all players are required to be on the field during the anthem. The new policy removes that requirement, allowing players who do not wish to stand to remain in the locker room.

Teams would be fined for violations.

The NFL Players Association, which was not included in league discussions on how to handle the anthem issue, threatened to challenge the policy if it was deemed a violation of its agreement with the league.

"The NFL chose to not consult the union in the development of this new 'policy'," the players' union said in a statement.

Former San Francisco 49ers quarterback Colin Kaepernick began the protests in 2016 as a way of drawing attention to police brutality, social injustice and racial inequity.

Kaepernick's protest followed a wave of deaths involving black men during confrontations with law enforcement officers.