The protests triggered by death of 46-year-old black man George Floyd in Minneapolis this week took a violent turn on Thursday as flames ripped through a Minnesota police station and seven protesters were shot in Kentucky as unrest spread across the United States over the deaths of black people during police encounters.

AFP reports, officers abandoned the building in the city of Minneapolis late on Thursday before demonstrators barged through barriers, breaking windows and chanting slogans. A fire broke out, which soon engulfed the structure.

Thousands joined the protests in Minnesota, after death of 46-year-old George Floyd who was arrested on suspicion of using a counterfeit banknote on Monday. A video taken by a bystander shows an officer kneeling on his neck as he is pinned to the ground. Floyd who was unarmed and handcuffed, pleaded that he could not breathe. He was soon after declared dead at a nearby hospital on Monday. Four policemen involved in the incident have been suspended, while the FBI is investigating the case.

The protests entered their fourth day on Friday and have spread beyond Minnesota, with protests breaking out in several states across the country, including Denver, Colorado and Phoenix.

In Kentucky, Louisville, seven people were hit by gunfire at a protest on Thursday over the death of Breonna Taylor,  a black woman who was shot by three white male police who entered her home in March, The New York Times reported. One of those wounded was in a critical condition, according to the Louisville Metro Police Department. It is not yet clear who fired the shots.

As unrest spread, President Trump tweeted: “These THUGS are dishonouring the memory of George Floyd and I won’t let that happen,” in apparent reference to protesters in Minnesota, adding the state’s governor has the backing of the military. “Any difficulty and we will assume control but, when the looting starts, the shooting starts.”

Twitter flagged the tweet for violating its rules on glorifying violence a few hours after it appeared.

Minnesota’s governor Tim Walz earlier called up 500 of the state’s National Guard, but after Trump tweeted he defended his decision not to put them on the streets as fire gripped the police station.

Outbreaks of violence have gripped the city as tensions rose since Floyd’s killing. On Wednesday, demonstrators clashed with law enforcement, looted stores and set fire to shops and a construction site. They were met with police tear gas and rubber bullets.

One person died of a gunshot wound, and police were reportedly investigating whether he was shot by a store owner.

The Justice Department on Thursday promised to carry out a “robust” investigation into Floyd’s death, saying they will make the case a top priority. Floyd’s family has demanded the officers present when he died face murder charges. All of them have been fired.

“You know, I want an arrest for all four of those officers tonight. A murder conviction for all four of those officers. I want the death penalty,” Floyd’s brother, Philonise Floyd, told CNN. “I have not slept in four days, and those officers, they’re at home sleeping,” he said.

(With inputs from AFP)