Officials in several states reinforced their National Guard presence as anger grew at increasingly aggressive tactics by the police.
Demonstrations continued across the United States on Sunday as officials braced for another night of destruction after a weekend of protests met by aggressive law enforcement response.
The fear and fury that had seized Minneapolis, where the death of yet another black man at the hands of the police last week set off days of protracted unrest, have now swept well beyond Minnesota, with tumultuous demonstrations from New York City and Los Angeles and dozens of cities in between.
The city of Philadelphia announced a 6 p.m. to 6 a.m. curfew after a day of violence and looting there, and Arizona’s governor declared a state of emergency and ordered a nightly 8 p.m. curfew that he said was “effective for one week.”
The actions came a day after hundreds of people were arrested across the country as clashes erupted between protesters and the police in dozens of states. In some cities, the authorities appeared to fire rubber bullets and other projectiles with little or no provocation. In New York City, two police vehicles surged forward into a crowd of demonstrators, some of whom were blocking the street and pelting the cars with debris.
At least 75 cities have seen protests in recent days, and the number mayors and governors imposing curfews — already more than two dozen — continued to grow. It is the first time so many local leaders have simultaneously issued such orders in the face of civic unrest since 1968, after the assassination of the Rev. Dr. Martin Luther King Jr.
National Guard soldiers were posted in Atlanta and Minneapolis, California moved troops into Los Angeles, and President Trump — out of public view but active on Twitter — urged governors, largely Democrats, to enact more and more forceful responses.
“Get tough Democrat Mayors and Governors,” Mr. Trump wrote on Twitter. “These people are ANARCHISTS. Call in our National Guard NOW. The World is watching and laughing at you and Sleepy Joe. Is this what America wants? NO!!!
Sunday’s protests marked the sixth day of outrage since George Floyd died while in police custody in Minneapolis on Monday. A cellphone video showed a white police officer — since fired and charged with third-degree murder — grinding his knee into Mr. Floyd’s neck for nearly nine minutes as he struggled to breathe.
Coming after months of restrictions to curb the coronavirus pandemic and the deep economic slowdown they have caused, with 40 million people out of work, the video of Mr. Floyd’s death brought a renewed outpouring of anguish over inequality and maltreatment that showed little sign of slowing.
In New York City, where chaotic confrontations between protesters and the police have resulted in dozens of injuries, hundreds of arrests, smashed storefronts and burned police vehicles, several groups of demonstrators were gathering again across the city on Sunday afternoon.
Hundreds of people had gathered at the Barclays Center arena in Brooklyn. Another large group marched south from Washington Square Park in Manhattan and crossed the Williamsburg Bridge into Brooklyn.
A demonstration at Bryant Park in Midtown Manhattan began with raised fists and a moment of silence. Many businesses had boarded up their windows in anticipation of trouble.
Target said it would temporarily close or shorten the hours of about 200 stores in the United States as protests continued to spread.
The Target store on Lake Street in Minneapolis, the location nearest to where Mr. Floyd died, was engulfed by unrest, badly damaged and looted last week. Images of the battered store have featured prominently in news coverage of the unrest in Minneapolis, where Target has its headquarters.
In a statement on its website Saturday night, Target said: “We are heartbroken by the death of George Floyd and the pain it is causing communities across the country. At this time, we have made the decision to close a number of our stores.”
One day after video showed them using stun guns on two black college students and then dragging them out of their car, two Atlanta police officers were fired for what the city’s mayor said constituted “excessive force.”
The mayor, Keisha Lance Bottoms, announced the dismissal of the two officers, whom she did not name, during a news conference on Sunday.
Ms. Bottoms said that three other officers who were involved in the episode had been reassigned to desk duty while the department reviews their actions.
“It was disturbing on many levels, the least of not which was that there clearly was an excessive use of force,” Ms. Bottoms said. “We understand that our officers are working very long hours under an enormous amount of stress, but we also understand that the use of excessive force is never acceptable.”
Ms. Bottoms said she had reviewed police body camera footage of the confrontation and that it should be released immediately. At least two bystanders also recorded video of the episode, and their recordings were widely shared on social media.
The actions of the Atlanta officers came amid intensifying scrutiny of how law enforcement was responding to demonstrators.
In Philadelphia, police in riot gear and an armored vehicle used pepper spray to try to repel rioters and looters, who breached a Target store and a Foot Locker store, according to photos posted on social media.
A wall of police officers blocked an entrance ramp to Interstate 676 in the city, where the mass transit system SEPTA announced that it was suspending service starting at 6 p.m. Sunday as part of a curfew.
In Miami, Mayor Francis Suarez of Miami gave out his cellphone number in a television interview with the local CBS station, urging people to contact him regarding any police issues. He had given his number out earlier to young protesters who sought him out after an afternoon news conference.
But in Chicago, the police superintendent, David Brown, excoriated the looters on Sunday as the Illinois governor, J. B. Pritzker, activated the National Guard at the city’s request.
“Let me be clear, last night was not a protest,” Mr. Brown said. “The people that came downtown were not there to exercise their First Amendment rights. That will not be tolerated.”
Chicago’s top law enforcement officer said that the police had shown great restraint during protests.
“I want to commend our officers for maintaining their composure throughout this whole ordeal,” he said.
President Trump said on Twitter on Sunday that the United States would designate a group of far-left anti-fascism activists as a terrorist organization, a declaration that lacked any clear legal authority, as his administration sought to blame the group for violent protests across the nation over the weekend.
“The United States of America will be designating ANTIFA as a Terrorist Organization,” Mr. Trump wrote.
The president has periodically criticized antifa, a contraction of the word “anti-fascist” that has come to be associated with a diffuse movement of left-wing protesters who engage in more aggressive techniques like vandalism.
But it was not clear that Mr. Trump’s declaration would have any real meaning beyond his characteristic attempts to stir a culture-war controversy, attract attention and please his conservative base.
“There is no authority under law to do that — and if such a statute were passed, it would face serious First Amendment challenges,” said Mary B. McCord, a former head of the Justice Department’s National Security Division. “But right now, the only terrorist authority is for foreign terrorist organizations.”
Nevertheless, in a statement after Mr. Trump’s tweet, Attorney General William P. Barr said the F. B. I. would use its partnerships with state and local police to identify violent protesters, whom he also called domestic terrorists.
“The violence instigated and carried out by antifa and other similar groups in connection with the rioting is domestic terrorism and will be treated accordingly,” Mr. Barr said.
But the American Civil Liberties Union condemned Mr. Trump’s vow in a statement from Hina Shamsi, its national security project director.
“As this tweet demonstrates, terrorism is an inherently political label, easily abused and misused,” Ms. Shamsi said. “There is no legal authority for designating a domestic group. Any such designation would raise significant due process and First Amendment concerns.”
Former Vice President Joseph R. Biden Jr., the presumptive Democratic presidential nominee, appeared in downtown Wilmington, Del.
