MINNEAPOLIS — Protesters set police cars ablaze, smashed businesses’ windows and skirmished with baton-wielding officers from Atlanta to Los Angeles, as anger over George Floyd’s death spread across the country.

Authorities were bracing for more violence Saturday, with some calling in the National Guard to beef up overwhelmed forces.

In Minneapolis, where Floyd died Monday after a white police officer pressed a knee into his neck and kept it there for more than eight minutes, Minnesota Gov. Tim Walz fully mobilized the state’s National Guard and promised a massive show of force to help quell unrest that has grown increasingly destructive.

“The situation in Minneapolis is no longer in any way about the murder of George Floyd,” Walz said. “It is about attacking civil society, instilling fear and disrupting our great cities.”

On Saturday, racially diverse crowds again took to the streets for peaceful protests in dozens of cities. Friday’s protests, too, had started calmly before many descended into violence.

At least two deaths were connected to the demonstrations; hundreds of people were arrested and police used batons, rubber bullets and pepper spray to push back crowds in some cities. Many departments reported officers were injured, while social media was awash in images of police using forceful tactics, throwing protesters to the ground, using bicycles as shields, and trampling a protester while on horseback.

Many protesters spoke of frustration that Floyd’s death was one more in a litany. It comes in the wake of the killing in Georgia of Ahmaud Arbery, who was shot after being pursued by two white men while running in their neighborhood, and in the middle of the coronavirus pandemic that has thrown millions out of work, killed almost 104,000 people in the U.S. and disproportionately affected black people.

On Friday, the officer who held his knee to Floyd’s neck was arrested and charged with third-degree murder and second-degree manslaughter — but that appeared to provide little balm. Many protesters are demanding the arrests of the three other officers involved.

Comments from President Donald Trump stoked the anger, when he fired off tweets criticizing Minnesota’s response, ridiculing protesters outside the White House and warning if they breached the fence, “they would have been greeted with the most vicious dogs, and most ominous weapons, I have ever seen.”

Trump also suggested his supporters would march outside the White House on Saturday.

“Tonight, I understand, is MAGA NIGHT AT THE WHITE HOUSE???” he tweeted.

Asked later whether the tweet might invite more racial violence, Trump demurred. “These are people that love our country,” he said of his supporters. “I have no idea if they were going to be here, I was just asking.”

On Saturday, in Tulsa, Oklahoma’s Greenwood District, the site of the 1921 Tulsa Race Massacre that left as many as 300 dead and the city’s thriving black district in ruins, protesters blocked intersections and chanted the name of Terence Crutcher, a black man killed by a police officer in 2016.

Leaders in many affected cities have voiced outrage over Floyd’s killing and offered sympathy for those who were protesting — but as unrest intensified, many said they would call in reinforcements.

The unrest prompted responses across the globe. A top Vatican cardinal, Peter Turkson who is from Ghana, urged pastors in the United States to plead for calm. U.S. national soccer player Weston McKennie wore an armband referencing Floyd’s death while playing in Germany.

Minnesota has steadily increased the number of National Guardsmen it says it needs to contain the unrest, and has now called up to 1,700. Governors in Georgia and Kentucky both activated the National Guard after protests there turned violent overnight.

A person was killed in downtown Detroit late Friday after someone in an SUV fired shots into a crowd of protesters, police said. And police in St. Louis were investigating the death of a protester who had climbed between two trailers of a FedEx truck and was killed when it drove away.

Atlanta saw some of the most extreme unrest. While crews in that city worked to clean up glass and debris from rioting the night before, a large electronic billboard on Saturday morning still carried the message, “If you love Atlanta PLEASE GO HOME,” echoing the mayor’s pleas.

“This is not in the spirit of Martin Luther King Jr.,” Atlanta Mayor Keisha Lance Bottoms said. “You are disgracing the life of George Floyd and every other person who has been killed in this country.”

Atlanta and downtown Los Angeles imposed overnight curfews that began Saturday night. Bottoms called the curfew an “unusual and extreme step.”

Protesters in Los Angeles clashed with police, setting several vehicles on fire, while protesters in Atlanta threw objects at officers guarding the Georgia governor’s mansion.

Gov. Brian Kemp was not in the home Saturday.

The New York Times contributed.