President Donald Trump has described protesters against the death of black man George Floyd in police custody in Minneapolis as thugs, vowing that "when the looting starts, the shooting starts".
Trump made the comments in a tweet after protesters, outraged by the death, torched a police station.
Earlier on Thursday, Trump said, "I feel very, very badly" about Floyd's death while handcuffed. "That's a very shocking sight."
It was a very different tone for Trump, often been silent in the face of white-on-black violence and with a long history of defending police.
Trump's language became more aggressive as violence boiled over on Thursday night in Minneapolis. "These THUGS are dishonoring the memory of George Floyd, and I won't let that happen," he tweeted. "Just spoke to Governor Tim Walz and told him that the Military is with him all the way. Any difficulty and we will assume control but, when the looting starts, the shooting starts. Thank you!"
Some activists doubt Trump has suddenly evolved on the issue of police brutality and instead see election-year political calculations.
"This is the first race-tinged case that I've ever heard him address" as president, said Reverend Al Sharpton, a civil rights activist and Trump critic. "So therefore, he cannot be upset when people feel that it's empty words because it is so out of character."
Trump has been silent on a number of high-profile police-involved killings, including that of Stephon Clark, a black man shot in 2018 by Sacramento police.
"This is something that is a local matter and that's something that we feel should be left up to the local authorities," then-White House press secretary Sarah Sanders said at the time.
He has never addressed the 2014 death of Eric Garner, who was placed in a chokehold by police trying to arrest him for selling loose cigarettes. Video of the encounter was viewed millions of times online and Garner's dying words, "I can't breathe," became a rallying cry for the Black Lives Matter movement. Trump has, however, invoked those words on several occasions to mock political rivals, even bringing his hands to his neck for dramatic effect.
Trump has a long history of injecting himself into racially sensitive cases. In 1989, he took out full-page newspaper ads calling for the death penalty for the Central Park Five, five young men of colour who were wrongly convicted of a brutal assault on a jogger. Trump has never apologised, telling reporters last year: "You have people on both sides of that".
Trump also spent years railing against NFL quarterback Colin Kaepernick for kneeling during the national anthem to protest racial injustice and police brutality.
Trump's tone has changed in recent weeks as he has repeatedly expressed dismay at footage of the killing of Ahmaud Arbery, the 25-year-old black man fatally shot in February in Georgia while jogging.
"You know, my heart goes out to the parents and the family and the friends," he told reporters this month. "It's a heartbreaking thing."
The president has notably left open the possibility of some other explanation, saying: "it could be something that we didn't see on tape".
Trump and his allies have been even clearer on the death of Floyd, who can be heard and seen on tape pleading that he couldn't breathe before he slowly stops talking and moving.
Trump "was very upset when he saw that video," White House press secretary Kayleigh McEnany said on Thursday. "He wants justice to be served."