US president Donald Trump has called protesters over the death of George Floyd in Minneapolis “thugs”, and vowed that “when the looting starts, the shooting starts”.

Mr Trump tweeted after protesters outraged by the death of the black man in police custody torched a police station.

Earlier on Thursday, Mr Trump had said he felt “very, very badly” about Mr Floyd’s death, which took place while he handcuffed and in the custody of Minneapolis police.

Mr Trump added: “That’s a very shocking sight.”

Twitter later added a public interest notice to Mr Trump’s tweet, regarding the comment about the response to looting.

The notice read: “This Tweet violates our policies regarding the glorification of violence based on the historical context of the last line, its connection to violence, and the risk it could inspire similar actions today.”

Mr Trump's tweet
A Twitter notice on Mr Trump’s tweet (Screengrab)

Mr Trump’s response is the kind of personal statement expected from a president in response to the video of a black man gasping for help as a white policeman pinned him to the street by the neck.

However, it was a very different tone for Mr Trump, who has often been silent in the face of white-on-black violence and has a long history of defending police.

Mr Trump’s language became more aggressive as violence boiled over in Minneapolis on Thursday night.

He wrote: “These THUGS are dishonoring the memory of George Floyd, and I won’t let that happen.

“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!”

Mr Trump and his allies have been questioning an officer’s conduct and calling for justice for Floyd. However, some activists doubt that Mr Trump has suddenly evolved on the issue of police brutality, and have pointed towards the fact there is an election due in the autumn.

The Rev Al Sharpton, a civil rights activist and Trump critic who has known the president for decades, said: “This is the first race-tinged case that I’ve ever heard him address” as president, “so therefore he cannot be upset when people feel that it’s empty words because it is so out of character.”

Mr Trump has been silent on a number of high-profile police killings, including that of Stephon Clark, a black man shot by Sacramento officers in 2018.

Protesters in Ohio
Protesters in Ohio (Barbara J Perenic/The Columbus Dispatch/AP)

“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.

Mr Trump 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 Mr Garner’s dying words, “I can’t breathe,” became a rallying cry for the Black Lives Matter movement.

Mr Trump has, however, invoked those words on several occasions to mock political rivals, even bringing his hands to his neck for dramatic effect.

The president 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 over a brutal assault on a jogger.

Minneapolis police death protests
Protests have taken place in Minneapolis for three nights in a row over Mr Floyd’s death (AP)

Mr Trump has never apologised, telling reporters last year: “You have people on both sides of that.”

The US president also spent years railing against NFL quarterback Colin Kaepernick for kneeling during the national anthem in protest over racial injustice and police brutality.

And he has even appeared to advocate for the rougher treatment of people in police custody, speaking dismissively of the police practice of shielding the heads of handcuffed suspects as they are being placed in patrol cars.

However, Mr 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.”

Mr Trump and his allies have been even clearer on the death of Mr Floyd, who can be heard and seen on tape pleading that he could not breathe before he slowly stops talking and moving.

The US leader “was very upset when he saw that video”, White House press secretary Kayleigh McEnany said. “He wants justice to be served.”

A recent Fox News poll found that just 14% of African Americans who are registered to vote have a favourable opinion of Trump, versus 75% who have a favorable view of Biden.