Three NFL players kneel for U.S. national anthem, stand for British anthem during Saints-Dolphins London game

Sunday's first NFL game was marked by a mix of protests amid the ongoing debate over how NFL players should exercise their voice during the national anthem.

The New Orleans Saints took a page from the Cowboys as the game against the Miami Dolphins began in London, kneeling together as a team initially, but then standing and locking arms as the U.S. national anthem was sung by Darius Rucker.

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Meanwhile, at least three members of the Dolphins -- Kenny Stills, Michael Thomas and Julius Thomas -- were seen kneeling during "The Star-Spangled Banner." All three then stood for the British anthem, "God Save the Queen," which was sung because the game was being played in England.

The anthem protests sprang into the spotlight last week when President Donald Trump took aim at the participating players during a speech in Alabama ahead of the NFL's week three Sunday games.

Trump's criticism has not abated since those initial comments. The president sent a new tweet criticizing NFL players for standing, calling into question the motivations of the protest.

"When you kneel for our #NationalAnthem, you aren't protesting a specific issue, you are protesting our Nation and EVERYTHING it stands for !!" he wrote in his latest tweet about the protests, sent Sunday morning.

SEE MORE: Trump says 'very important' NFL players stand for National Anthem

Former San Francisco 49ers quarterback Colin Kaepernick, who originally spurred the demonstrations but is not currently playing in the NFL, said he began kneeling for the anthem because of American oppression.

"I am not going to stand up to show pride in a flag for a country that oppresses black people and people of color," Kaepernick said in an interview in 2016. "To me, this is bigger than football and it would be selfish on my part to look the other way. There are bodies in the street and people getting paid leave and getting away with murder."

The president has called on the NFL to institute a rule forcing players to stand during the anthem.