NEW YORK — The week started with scenes from a cellphone video of an African-American man lying on the ground being fatally shot by a Louisiana police officer, and a Facebook Live feed of a woman in Minnesota narrating after her African-American boyfriend was killed by an officer during a traffic stop.
It culminated with horrific live television coverage of police officers being gunned down by at least one sniper at what had been a peaceful march protesting the police shootings.
Police said officers were also targeted Thursday and Friday in Georgia, Missouri, and Tennessee by suspects who said they were angry about police violence against blacks.
In Tennessee, a man was accused of shooting indiscriminately at passing cars and police on a highway, killing a woman and injuring three people, including a police officer. The suspect, Lakeem Keon Scott, who is black, was wounded and has not been charged. All the victims were white.
Officers were wounded in the Georgia and Missouri attacks but are expected to recover.
The convulsive events further divided a nation already torn over race and law enforcement, raising anguished pleas for unity and echoes of the protests and divisions of the late 1960s and early 1970s.
“Even in the 1960s and 1970s, when there was a lot of tension around policing and civil rights and the antiwar movement, we’d never seen anything like what happened in Dallas,” said Darrel Stephens, the executive director of the Major Cities Chiefs Association and an instructor at Johns Hopkins University.
David O. Brown, the Dallas police chief, said the sniper suspect who was killed after a standoff with police had told negotiators that he was upset at white people.
Across the country, people poured onto city streets and gathered for vigils, protests and marches Friday in response to the violence. They railed against police brutality and the deaths of the two men fatally shot by police, while also grieving for the five police officers slain in Dallas late Thursday.
In Washington, D.C., people gathered outside the White House and in Philadelphia they came together outside City Hall. There were demonstrations in Baltimore, Atlanta, Buffalo and Birmingham, Ala. Even across the Atlantic, in London, some 300 people gathered, raising closed fists as they protested police brutality, the BBC reported.
Protesters continued to speak out against the deaths of Alton Sterling of Baton Rouge, La., and Philando Castile of St. Paul, both black men whose deaths at the hands of police were captured on video in the last week and broadcast widely.
Some marches brought heightened security as the shooting in Dallas raised fears that other public gatherings could be targeted.
On social media Friday, there were salutes to the sniper, blame of the news media for dividing the nation, charges that black protesters had spread hysteria, and laments that the country is headed toward an unbridgeable divide.
The mother of the son of the black man killed by white Louisiana police officers said Friday that she grieved with the families of five officers killed in Dallas.
‘‘Now, I'm walking a mile with them. We’re bearing the same shoes right now,’’ said Quinyetta McMillon.
Sterling, 37, was killed Tuesday in Baton Rouge during a struggle with two police officers outside a convenience store where he was selling CDs. Cellphone video of his shooting was posted online and set off angry protests in Baton Rouge and beyond. The Justice Department has opened a civil rights investigation into Sterling’s shooting.
In Minnesota on Wednesday, Diamond Reynolds live-streamed to Facebook a video in the immediate aftermath of the fatal shooting of her boyfriend, Castile, by police.
Governor Mark Dayton of Minnesota asked residents Friday to remain peaceful as they protest the fatal police shooting of Castile in a car. Dayton also said Friday that he stood by statements he made a day earlier that police probably wouldn’t have opened fire had Castile been white.
In Atlanta, thousands marched through the streets, gathering in front of the CNN Center downtown, the Atlanta Journal-Constitution reported. Television images showed a growing crowd facing a line of police officers.
‘‘This is no time to be calm. You would be a fool to be calm if you are under genocide,’’ Rev. Francys Johnson, president of the Georgia NAACP, told the crowd. ‘‘Racism is not a black problem, it’s a white problem.’’
Sir Maejor, a Black Lives Matter organizer, said the rally in Atlanta Friday was scheduled before the Dallas shooting.
‘‘Black Lives Matter doesn’t condone shooting law enforcement. But I have to be honest: I understand why it was done,’’ Maejor said. ‘‘I don’t encourage it, I don’t condone it, I don’t justify it. But I understand it.’’
Black Lives Matter began in 2013 after black teenager Trayvon Martin was shot to death by George Zimmerman, a one-time community watch volunteer in Florida.
In Washington, D.C., more than 50 people held a vigil in front of the Department of Justice before marching to the White House. ‘‘Stop killing us’’ and ‘‘Police violence is terrorism’’ their signs read.