Minneapolis -- A thousand more National Guard soldiers were mobilized Saturday as violent protests over the death of an unarmed black man during an arrest in Minneapolis erupted across the United States.

Murder charges laid against the officer Friday failed to quell seething anger as riots against police racism raged from New York to Los Angeles in one of the worst nights of civil unrest in America in years.

Demonstrators ignoring a curfew clashed with police for a fourth straight night in the midwestern city of Minneapolis, where fires burned out of control, looters roamed freely and protesters staged cat-and-mouse clashes with law enforcement.

Minnesota National Guard Major General Jon Jensen told a press conference early Saturday that the state's governor had authorized the deployment of an extra 1,000 soldiers to help police control the situation.

The state has become the epicenter of violence since George Floyd died there in an arrest by an officer who pinned him to the ground for several minutes by kneeling on his neck.

Derek Chauvin was charged Friday with one count of third-degree murder -- unintentionally causing a death -- and one count of negligent manslaughter.

"This case is now ready, and we have charged it," said county prosecutor Mike Freeman as outrage grew over the latest death of an African American in police custody.

But the charges failed to calm a shaken nation whose deep wounds over racial inequality have been torn open anew.

In Atlanta, police cruisers were attacked and set ablaze as rallies spun out of control, while in the capital Washington protesters collided with Secret Service agents in heated midnight scenes in front of the White House.

President Donald Trump said he watched "every move" the agents took and "couldn't have felt more safe."

In a tweet, he wrote: "They let the 'protesters' scream & rant as much as they wanted, but whenever someone got too frisky or out of line, they would quickly come down on them, hard - didn't know what hit them."

Protests took hold in a swathe of cities including Boston, Dallas, Denver, Des Moines, Houston, Las Vegas, Memphis, and Portland.

'Chaos'

Authorities imposed a curfew Friday in Minneapolis after three nights of protests left parts of the city in flames.

But the demonstrators, many wearing masks to prevent the spread of coronavirus, defiantly remained on the streets, facing off with police who fired tear gas and flashbangs in efforts to regain control.

Looting was widespread, with images showing people coming out of shops carrying armfuls of goods.

Officers were shot at by protesters, Minnesota's governor Tim Walz told reporters early Saturday.

"This is not about George's death. This is not about inequities that were real. This is about chaos," he said.

But that view was not shared on the streets. "I need you to look in my eyes and feel me," said protester Naeema Jakes. "This is pain, this is hurt."

Tougher charges

Floyd's relatives -- who spoke Friday with President Trump -- welcomed news of the officer's arrest as a "step on the road to justice."

But they said they hoped for tougher charges and action against the other officers involved in Floyd's detention and death.

"We want a first-degree murder charge. And we want to see the other officers arrested.

"The pain that the black community feels over this murder and what it reflects about the treatment of black people in America is raw and is spilling out onto streets across America," they said in a statement.

Freeman said the three other officers present when Floyd died were also under investigation, and that he anticipated charges would be laid against them.

All four were fired from the police department Tuesday after video surfaced of the arrest.

'Cry and cry some more'

Protesters gathered outside officer Chauvin's vandalized Minneapolis home Friday, raising placards to passing cars and chanting Floyd's name.

"All I can do is just cry, and cry some more," Tara Balian, 39, told AFP. "It's taken this long for people to realize that black lives matter."

Several protesters chanted "I can't breathe" -- Floyd's words as Chauvin's knee pressed on his neck.

Trump, after attacking the protesters as "thugs" and threatening to send in federal troops to deal harshly with them, shifted tone Friday, announcing he had called Floyd's family to express his "sorrow."

"I understand the hurt, I understand the pain. People have really been through a lot," said the president, who stands accused of stoking tensions with a series of provocative tweets.

Former vice president Joe Biden, who is challenging Trump for the White House in November's election, also spoke to Floyd's family.

He called for justice and said it was time to heal the "open wound" of systemic racism in the United States.