Minnesota Governor Tim Walz says he expects justice for the death of an unarmed black man in Minneapolis police custody “will be swift”.
There have been days of protests, looting and arson after an officer was filmed kneeling on George Floyd’s neck even as he said he could not breathe.
Mr Walz said justice for the officers involved in Mr Floyd’s death “will come in a timely manner” and “will be fair”.
Former President Barack Obama has said this “can’t be ‘normal'” for America.
The case has added to nationwide anger over police killings of black Americans.
On Thursday, during the third night of protests over Mr Floyd’s death, a police station was set alight. A number of buildings have been burned, looted and vandalised in recent days, prompting the activation of the state’s National Guard troops.
The governor condemned the arson and damage in recent days, saying: “We cannot have the looting and the recklessness that went on.”
“I need to ask Minnesotans: those in pain, and those who feel like justice has not been served yet, you need to help us create this space so that justice will be served, ” Mr Walz told reporters on Friday.
Mr Obama said on Friday: “This shouldn’t be ‘normal’ in 2020 America. It can’t be ‘normal’. If we want our children to grow up in a nation that lives up to its highest ideals, we can and must be better”.
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President Donald Trump earlier said “thugs” were dishonouring Mr Floyd’s memory and called on the National Guard to restore order.
Mr Floyd’s family have demanded that the four police officers implicated in his death face murder charges. Prosecutors have said they are still gathering evidence.
The team was released an hour later, after the governor apologised for the arrest.
There have also been demonstrations in other US cities, including New York, Los Angeles, Chicago, Denver, Phoenix and Memphis.
What is the latest in Minneapolis?
On Thursday, protesters gathered outside the police department’s 3rd Precinct, the epicentre of the unrest.
Officers fired tear gas and rubber bullets in an attempt to disperse the crowd. But the cordon around the police station, which is near where Mr Floyd died, was breached by protesters, who set fire to it and two other nearby buildings as the officers withdrew.

Minneapolis Mayor Jacob Frey said there had been no choice but to evacuate the police station, adding: “The symbolism of a building cannot outweigh the importance of life, of our officers or the public.”
He called the unrest “unacceptable”, but recognised there was “a lot of pain and anger”.
He spoke after a tweet from Mr Trump blamed Thursday’s violence on a “lack of leadership” in Minneapolis and warned that he would send in the National Guard and “get the job done right” if Mr Frey failed to restore order.
National Guard personnel are normally under state control, although they can be put under federal control in emergencies.
Mr Trump also tweeted: “Any difficulty and we will assume control but, when the looting starts, the shooting starts.”
On Friday, the White House Twitter account quoted the president’s tweet on looting and shooting.
The historical context arises from riots in Miami in 1968. A federal task force found that the use of the phrase about looting by the Miami police chief at the time was a prime factor in the discontent that triggered the unrest.

Sirens, smoke, and no end in sight
Analysis by Jessica Lussenhop, BBC senior staff writer, Minneapolis
The “twin cities” of Minneapolis and St Paul, Minnesota heaved with unrest and destruction overnight.
Several areas that have no geographical significance to Floyd’s death are now seeing damage, and shops all over the region closed and barricaded their doors.
Protesters in the streets want one thing: the arrest and prosecution of former Minneapolis police officer Derek Chauvin, whose knee was pressed into Floyd’s neck for several minutes before he died.
But at a press conference on Thursday, Hennepin County Attorney Mike Freeman was noncommittal, promising only a “robust and meticulous” investigation. Both the FBI and the Minnesota Bureau of Criminal Apprehension are investigating.
It’s unclear whether charges would actually bring the violence to a halt.
Developments here are swift and chaotic. Friday morning broke with news that several fires had been set before dawn in Minneapolis and that state police arrested a CNN news crew on live television.
The air in this relatively quiet Midwestern metropolis is filled with sirens and smoke, and it seems there is no end in sight.


On Friday, Mr Walz said: “Our community, especially our black community, is hurting beyond words,”
“Minneapolis and St Paul are on fire. The fires still smoulder in our streets.
“The ashes are symbolic of decades and generations…of pain, of anguish, unheard, much like we failed to hear George Floyd as he pleaded for his life, as the world watched, by people sworn to protect him, his community, our state.”
What has been the reaction?
The four policemen involved have been fired, and the mayor has called for criminal charges against the officer seen pinning Mr Floyd.
Speaking through tears, Mr Floyd’s brother, Philonise, told CNN on Thursday the officers who “executed my brother in broad daylight” must be arrested and that he was “tired of seeing black men die”.

Mr Trump “was very upset” when he saw the footage of Mr Floyd’s death, White House press secretary Kayleigh McEnany told reporters on Thursday.
A number of celebrities, including John Boyega and Beyonce, have also expressed outrage over the incident.
The incident echoes the case of Eric Garner, who was placed in a police chokehold in New York in 2014. His death became a rallying cry against police brutality and a catalyst in the Black Lives Matter movement.
Where else have there been protests?
There were also chaotic scenes during rallies in Denver, Colorado and in Columbus, Ohio.

The statehouse in Denver was put under lockdown after gunfire was heard, while in Columbus demonstrators reportedly broke some of the statehouse’s windows before being dispersed by police.
Seven people were also shot in Louisville, Kentucky, at a protest over the death of Breonna Taylor, who was shot by three white police officers in March.
What happened to George Floyd?
Officers responding to reports of the use of counterfeit money approached Mr Floyd in his vehicle on Monday.
According to police, he was told to step away from the car, physically resisted officers and was handcuffed.
Video of the incident does not show how the confrontation started, but a white officer can be seen with his knee on Mr Floyd’s neck, pinning him down.
Mr Floyd can be heard saying “please, I can’t breathe” and “don’t kill me”.


The city has identified the four officers involved as Derek Chauvin, Tou Thao, Thomas Lane and J Alexander Kueng.
The Minneapolis Police Officers’ Federation said the officers were co-operating with the investigation.
The Minnesota police handbook states that officers trained on how to compress the neck without applying direct pressure to the airway can use a knee under its use-of-force policy. This is regarded as a non-deadly-force option.

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