Protesters have clashed with police in cities across the US over the killing of an unarmed African-American man at the hands of officers in Minneapolis.

Hundreds of people rallied outside the White House, which was briefly put under lockdown on Friday, demanding justice over the death of George Floyd.

Demonstrations have been taking place in Minnesota, New York and California.

A former Minneapolis police officer has been arrested and charged with murder over Mr Floyd's death in custody.

Derek Chauvin, who is white, was shown in footage kneeling on 46-year-old Mr Floyd's neck on Monday. He and three other officers have since been sacked.

Mr Chauvin, 44, is due to appear in court in Minneapolis for the first time on Monday.

President Donald Trump has described the incident as "a terrible, terrible thing" and said he had spoken with Mr Floyd's family, whom he described as "terrific people".

What happened during the protests?

On Friday evening, crowds gathered near the White House in Washington, DC, waving photographs of Mr Floyd and chanting "I can't breathe" - invoking his last words and those of Eric Garner, a black man who died after being held in a police chokehold in New York in 2014.

The White House was then temporarily placed on lockdown, with the US Secret Service closing entrances and exits.

Curfews were ordered for the Twin Cities of Minneapolis-Saint Paul, from 20:00 to 06:00 on both Friday and Saturday evening. But further gatherings of protesters were reported after the curfew had come into effect, and buildings and vehicles were later set alight.

There were violent clashes between protesters with police in several cities, including New York, Los Angeles, Chicago, Denver, Houston, Louisville, Phoenix, Columbus and Memphis.

In Atlanta, buildings were vandalised and a police vehicle was set alight as protesters gathered near the offices of news broadcaster CNN.

In Dallas, officers launched tear gas canisters after they were pelted with stones.

While Mr Chauvin has been charged with third-degree murder and second-degree manslaughter over his role in Mr Floyd's death, the protesters want the other officers involved to face justice.

The case has reignited US anger over police killings of black Americans, and the nationwide protests follow days of looting and arson in Minneapolis.

On Thursday, during the third night of protests, 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.

What did the prosecutor say?

Hennepin County Prosecutor Mike Freeman said he "anticipates charges" for the three other officers but would not offer more details.

Mr Freeman said his office "charged this case as quickly as evidence has been presented to us".

"This is by far the fastest that we've ever charged a police officer," he noted.

According to the criminal complaint, Mr Chauvin acted with "a depraved mind, without regard for human life". 

How did George Floyd die?

The full report by the county medical examiner has not been released, but the complaint states that the post-mortem examination did not find evidence of "traumatic asphyxia or strangulation".

The medical examiner noted Mr Floyd had underlying heart conditions and the combination of these, "potential intoxicants in his system" and being restrained by the officers "likely contributed to his death".

The report says Mr Chauvin had his knee on Mr Floyd's neck for eight minutes and 46 seconds - almost three minutes of which was after Mr Floyd became non-responsive.

Nearly two minutes before he removed his knee the other officers checked Mr Floyd's right wrist for a pulse and were unable to find one. He was taken to the Hennepin County Medical Center in an ambulance and pronounced dead around an hour later.

The Minnesota police handbook states that officers trained on how to compress a detainee's 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.

What has the president said?

At the White House on Friday, Mr Trump said he had asked the justice department to expedite an investigation it announced on Friday into whether any civil rights laws were violated in Mr Floyd's death.

The president also said "looters should not be allowed to drown out the voices of so many peaceful protesters".

Earlier, he described the rioters as "thugs" who were dishonouring Mr Floyd's memory.

Social media network Twitter accused Mr Trump of glorifying violence in a post that said: "When the looting starts, the shooting starts."

What's the reaction?

Mr Floyd's family and their lawyer, Benjamin Crump, said that the arrest was "welcome but overdue".

The family said they wanted a more serious, first-degree murder charge as well as the arrest of the other officers involved.

The statement called for the city to change its policing, saying: "Today, George Floyd's family is having to explain to his children why their father was executed by police on video."

Former US President Barack Obama also weighed in, saying: "This shouldn't be 'normal' in 2020 America."

His statement added: "If we want our children to grow up in a nation that lives up to its highest ideals, we can and must be better."

Minnesota Governor Tim Walz said the arrest was "a good first step toward justice".

What happened in the arrest?

Officers suspected Mr Floyd had used a counterfeit $20 note and were attempting to put him in a police vehicle when he dropped to the ground, telling them he was claustrophobic.

According to police, he 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".

A former local nightclub owner has said Mr Chauvin and Mr Floyd both worked as bouncers at her venue in south Minneapolis up until last year, though it is unclear if they knew one another.