Prosecutors in Minnesota on Wednesday upgraded charges against the US police officer primarily implicated in the killing of a handcuffed black man, and charged three other officers over the death, which has ignited nationwide protests.
With a key demand met, demonstrators vowed to press on in the fight against racism, staging protests in cities from New York to Los Angeles after the new charges were announced.
Pressure on Trump mounted as his former Pentagon chief Jim Mattis launched a searing broadside, accusing the Republican leader of trying to "divide" America.
In Minnesota, prosecutors had initially charged 44-year-old Derek Chauvin -- the white officer filmed kneeling on the neck of George Floyd for nearly nine minutes -- with third-degree murder.
But they said Wednesday they were upgrading the charge, roughly akin to manslaughter, to second-degree murder, which does not involve premeditation but carries stiffer penalties.
"I believe the evidence available to us now supports the stronger charge of second-degree murder," Minnesota attorney general Keith Ellison said.
Chauvin's three colleagues at the scene of Floyd's May 25 arrest for allegedly seeking to buy cigarettes with a counterfeit bill are accused of being complicit in the killing.
Tou Thao, 34, J. Alexander Kueng, 26, and Thomas Lane, 37, were charged with aiding and abetting second-degree murder, and taken into custody.
The arrest of all four officers involved has been a focus for tens of thousands of protesters who have marched the streets of dozens of US cities for the past nine days, often defying curfews to condemn police brutality and demand racial justice.
Minnesota Governor Tim Walz said the upgraded charges and arrests presented a chance to "come back to the issue at hand... systemic racism and the lack of accountability."
"This is probably our last shot, as a state and as a nation, to fix this systemic issue," he said.
Floyd's family, in a statement thanking protesters, called the arrests and new charges a "bittersweet moment" -- and a "significant step forward on the road to justice."
They urged Americans to continue to "raise their voices for change in peaceful ways."
At a protest in Manhattan, Brian Clark said the charges were "a good start" but vowed demonstrators would "exercise our right to protest until every black person gets the justice they deserve."
"It's not enough," added fellow demonstrator Elijah B., who did not give his last name.
"This could have happened a week ago... it wasn't until people started marching on the streets and started tearing things that people started to pay attention."
Thousands took to the streets in both Hollywood and downtown Los Angeles. A large group also protested at the US Capitol.
Former president Barack Obama applauded the "change in mindset" he sees among Americans demanding racial justice, and urged the nation to "take the momentum that has been created as a society, as a country, and say 'Let's use this' to finally have an impact."
'Law and order'
While condemning Floyd's death, Trump has adopted a tough stance towards the protesters, saying they include many "bad people" and calling on governors to "dominate the streets."
"We need law and order," he repeated on Wednesday.
Mattis ripped into Trump, calling him "the first president in my lifetime who does not try to unite the American people -- does not even pretend to try."
"Instead, he tries to divide us," the retired Marine general said in a blistering statement posted online by The Atlantic.
Trump has raised the possibility of invoking the Insurrection Act to deploy active duty troops to quell unrest.
But Mattis' successor Mark Esper said that option should only be used as "a matter of last resort and only in the most urgent and dire of situations."
"We are not in one of those situations now. I do not support invoking the Insurrection Act," said the current defense secretary.
White House spokeswoman Kayleigh McEnany said Wednesday that the act remains "a tool available" to the president, who is facing a tough reelection battle in November.
"The president wants to protect America's streets," McEnany said. "We cannot have burning churches. We cannot have police officers that are shot. We cannot have businesses that are looted and destroyed."
Trump meanwhile denied media reports that he was rushed for his safety to the White House bunker while protests raged in the streets outside.
"It was a false report," Trump told Fox News Radio, before saying that he did go into the secure area for an "inspection" and only for a "tiny, little, short period of time."
Reports of Trump taking shelter sparked a wave of online mockery, which is believed to have contributed to his decision on Monday to make a controversial visit to a partly damaged church near the White House.
Police violently dispersed mostly peaceful crowds of protesters to clear a path for Trump, and the photo opportunity was widely condemned.
Curfews remained in place Wednesday in cities including New York, Los Angeles and Washington, though they were slightly loosened.
Los Angeles and Washington both delayed the start of their curfews by several hours, compared to previous nights.
Former president Jimmy Carter called on "people of power, privilege and moral conscience" to bring an end to racial discrimination.
"We need a government as good as its people, and we are better than this," the 95-year-old Carter said in a statement.