President Donald Trump says federal law enforcement will be sent to Kenosha, Wisconsin, following unrest sparked by the police shooting of a black man.
Jacob Blake, 29, was shot and injured by police on Sunday as he leaned into his car and as his children watched.
Protests have been ongoing for several nights, and on Tuesday, two people were shot dead and another was injured. A teenager has been charged with murder.
Mr Blake is recovering in hospital and is conscious, his family say.
But his lawyers say it will take “a miracle” for him to walk again.
The protests over Mr Blake’s shooting have at times turned violent, causing damage to property.
Tuesday night’s incident was believed to have involved protesters against Mr Blake’s shooting and armed men guarding a petrol station.
Hours later, police in neighbouring Illinois said they had arrested a 17-year-old on suspicion of first-degree murder.
Announcing his move in a tweet on Wednesday, Mr Trump said: “We will NOT stand for looting, arson, violence, and lawlessness on American streets. My team just got off the phone with Governor Evers who agreed to accept federal assistance (Portland should do the same!).”
He added: “TODAY, I will be sending federal law enforcement and the National Guard to Kenosha, WI to restore LAW and ORDER!”
Shortly following Mr Trump’s tweet, Mr Evers, the Wisconsin governor, said he had authorised 500 National Guard troops to support law enforcement efforts.
Kenosha Mayor John Antaramian said the FBI, Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), US Marshals as well as police across the state were already involved in efforts to quell the unrest.
What’s happening in Kenosha?
Hours after Mr Blake was shot on Sunday, hundreds rallied outside Kenosha’s police headquarters. As the protests went on, cars were set alight, armed robberies were reported and a night-time curfew was eventually put in place.
Protesters said police and troops used tear gas, rubber bullets and smoke bombs.
On Tuesday, hundreds of protesters marched through the city again. A small group threw fireworks and water bottles at police, who responded with rubber bullets and tear gas.
A spokesman for the Wisconsin Professional Police Association told the BBC individuals and groups were exercising their own form of vigilantism because law enforcement was spread very thin across the city.
On social media, footage showed a man with a rifle being chased by a crowd before he fell to the ground and appeared to fire at them. Other video shows armed civilians, many dressed in military fatigues, congregating outside businesses they said they were protecting.
During Wednesday’s news conference, Kenosha Police Chief Daniel Miskinis confirmed that a 17-year-old from Antioch, Illinois, was arrested over the deaths of a 26- and 36-year-old during the protests. The injured individual is also 26 years of age, and is expected to recover, he said.
Sheriff David Beth announced that a new curfew would be implemented from 19:00-07:00 and last until Sunday.
He said that while no-one in law enforcement opposed peaceful protests – noting that he himself participated in a demonstration last month – “we are not going to put up with what we saw Monday night”.
The sheriff also said that there had been calls for him to allow civilians to help with law enforcement – a process known as deputising.
“What happened last night was probably the perfect reason why I wouldn’t,” he said. The sheriff added that he was not certain but believed the individual involved in the two deaths belonged to a group that wanted to be deputised.
Mayor Antaramian told reporters on Wednesday: “I am here today basically to, number one, inform everyone that we are not planning on letting this violence continue.
“Number two, we are going to work together to resolve the racial issues in our community, and we are going to make that work.”
What other reaction has there been?
On Tuesday, Mr Blake’s mother, Julia Jackson, said that her son had been “fighting for his life”, but that if he “knew what was going on as far as that goes, the violence and the destruction, he would be very unpleased”.
Protests have also spread to a number of other cities, including Portland, Oregon and in Minneapolis, Minnesota, where the police killing of unarmed black man George Floyd in May sparked Black Lives Matter protests across the US and globally.
The Toronto Raptors basketball team, who won last year’s NBA championship, have discussed potentially boycotting an upcoming conference semi-final game in response to Mr Blake’s shooting.
Player Norman Powell said the situation had gotten to a point where just saying “Black Lives Matter” was not enough.
“I think everybody’s at the point of sitting up here and saying ‘Black Lives Matter’ and sitting up having discussions and Zoom calls… That’s not getting the job done. Taking a knee for the anthem, that’s not getting the job done.”