Last updated on .From the section American football

NFL teams have been "taking the knee" during the American national anthem as a form of protest

Houston Texans' owner has apologised for describing NFL players as "inmates running the prison" in reference to protests against racial injustice.

The protests have spread throughout the league since Colin Kaepernick sat, before later opting to kneel instead, during the US national anthem in 2016.

Bob McNair made his comments during a league meeting held to discuss the issue in New York last week.

On Friday he said he "regretted" using the expression.

"I never meant to offend anyone and I was not referring to our players," a statement added.

"I used a figure of speech that was never intended to be taken literally. I would never characterise our players or our league that way and I apologise to anyone who was offended by it."

After last week's meeting, the NFL said it will not force its players to stand during the national anthem.

The league's commissioner Roger Goodell said he would "encourage" players to stand, but would not punish them if they refused to do so.

Kaepernick, 29, has been without a team since he opted out of his contract with the San Francisco 49ers in March.

He has filed a grievance against NFL team owners he believes are conspiring to not hire him because of his protests against racial injustice.