NEW YORK - President Donald Trump on Friday lobbed barbs at protesters who kneel during the national anthem, after NFL quarterback Drew Brees apologized for remarks he made about the practice.

Brees said this week he would "never agree with anybody disrespecting the flag," referring to the possibility of players kneeling during the "Star-Spangled Banner" in the upcoming NFL season. Brees apologized Thursday, saying his words "lacked awareness and any type of compassion or empathy."

The kneeling pose, popularized by NFL quarterback Colin Kaepernick, has become a symbol of the fight for racial justice in the United States.

Trump tweeted on Friday that Brees "should not have taken back his original stance."

"We should be standing up straight and tall, ideally with a salute, or a hand on heart," Trump wrote. "There are other things you can protest, but not our Great American Flag - NO KNEELING!"

The kneeling pose has been seen at protests in cities across the country in the wake of the death of George Floyd, an unarmed black man, while in police custody in Minneapolis.

Brees' initial remarks angered top athletes, who objected to equating the protest with disrespecting the American flag.

"You literally still don't understand why Kap was kneeling on one knee??" NBA great LeBron James posted on Twitter earlier this week. "Has absolute nothing to do with the disrespect of Flag of United States and our soldiers(men and women)."

Kaepernick popularized the move in 2016, appearing on NFL sidelines first sitting, and later kneeling, during the customary pre-game airing of the U.S. national anthem.

Trump was an early critic of the protest, and in 2017 Vice President Mike Pence walked out of an NFL game between the 49ers and the Indianapolis Colts when some of the players knelt on the sidelines during the anthem.