Law enforcement form a line across Interstate 94 on Saturday, July 9, 2016, in St. Paul, Minn., in response to protesters who blocked the highway. The protesters were rallying in response to the death of Philando Castile, who was shot and killed by a suburban St. Paul police officer on July 6. (Joe Danborn/AP)

This post has been updated.

Protests escalated late Saturday in the states where police shootings of black men this week fueled outrage, with marchers shutting down a Minnesota highway and prominent Black Lives Matter activist Deray McKesson among dozens taken into police custody in Baton Rouge.

Hundreds of demonstrators facing hundreds of officers in riot gear sat on Interstate 94 outside St. Paul, Minn., blocking traffic.  The police used smoke bombs and flash bangs to disperse the crowd, which eventually broke up after several hours. Some protesters had thrown rocks and plastic water bottles at officers, and the St. Paul Police Department tweeted that five officers were injured, including one struck on the head with a large piece of concrete.

McKesson, a Baltimore-based activist who traveled to Baton Rouge, was one of 34 people taken into custody around 11 p.m. Saturday night in what fellow activists described as a physically violent arrest. Tensions also had been flaring in Baton Rouge after Black Panthers confronted Louisiana state troopers.

In San Antonio, police were disturbed after shots were fired at their headquarters shortly before 10 p.m. local time. Authorities were looking for a man seen running from an alley where shell casings were discovered, and a bomb squad examined a nearby car.

No one was injured, but the incident echoed the fatal shooting of five police officers in Dallas by an African American gunman who, by police accounts, was consumed with racially driven rage over recent officer-involved shootings of black men.

“It’s alarming right now,” San Antonio Police Chief William McManus told reporters late Saturday. “It’s not the first time our building has been shot at, but it’s too coincidental that it’s around the time that officers are being threatened in cities around the country, especially here in Texas.”

Demonstrations decrying police killings continued across the nation earlier in the day.

In San Francisco, protesters chanting “Black Lives Matter” blocked a ramp to the Bay Bridge. In Chicago, demonstrators planned more marches after staging a “die-in” in front of President Obama’s house.

And in Dallas, quiet grief: a candlelight vigil, piles of flowers and honor guard salutes for the fallen officers.

Scenes of common rage and confrontation have flared before on American streets — resonating across the country after deaths in Baltimore and Ferguson, Mo. — as the rallying cry of “Black Lives Matter” unites generations, ranging from those who remember the civil rights struggles of the 50s and 60s to those who grew up learning how to master social media as a powerful tool for activism.

But the latest wave of protests and memorials — leading to more than 100 arrests in more than a dozen cities — appear to carry a deeper sense of a country increasingly at odds with itself and fearing what could come next.

“History is a dance. We go backwards and forwards,” said Dallas Mayor Mike Rawlings. “And now we can dance toward progress, or dance toward chaos.”

Even as buildings were bathed in blue in honor of the police officers killed by the Dallas sniper — the deadliest day for U.S. law enforcement since 9/11 — police agencies were on heightened safety alerts after three officers were shot Friday on the job in Missouri, Tennessee and Georgia.

It remains unclear whether all three shootings had links to the wider protests touched off by the deaths earlier this week of Alton Sterling, of Baton Rouge, and Philando Castile, of St. Paul, Minn., — both black men whose killings by police were captured on video circulated widely on social media. Yet it was enough for some police departments, including Washington, to call for two-person patrols for added security, and Obama to offer words of unity for a second consecutive day.

“As painful as this week has been, I firmly believe that America is not as divided as some have suggested,” Obama said Saturday while in Poland for a NATO summit. “Americans of all races and all backgrounds are rightly outraged by the inexcusable attacks on police, whether it’s in Dallas or anyplace else.”

Just three weeks ago, people gathered around the globe joined in collective mourning for 49 people killed in an Orlando nightclub by a gunman possibly inspired by Islamist militants. Now, the world watched again as American cities were pitched by anger.

Baton Rouge was among the main flash points. More than 100 people gathered Saturday in the parking lot of the Triple S Food Mart, where Sterling was fatally shot. Police were not visible on the streets, but a helicopter circled above.

Across the street, Rena Jones, 36, set up a computer and printer under a small white tent, selling $12 t-shirts printed on the spot with images of Sterling and Castile. On the back of the shirt, Jones has printed “All Lives Matter.” She said she will print really anything you want instead, but “it costs a little extra.”

In earlier protests that ran past midnight, at least 200 protesters massed outside of police headquarters and gathered on streets, holding their arms in the air and chanting, “Hands up, don’t shoot.” One group of protesters joined in a song drawing back to protests generations earlier: “We Shall Overcome.”

Police — some in riot gear — moved in after ordering crowds to disperse. At least 31 people were taken into custody, police said. At least one woman was dragged away in handcuffs.

Meanwhile, protesters gathered around a makeshift memorial at the Triple S Food Mart where Sterling was shot earlier this week. Lines of cars blasted hip-hop from their windows as they slowly cruised by the traffic-jammed intersection. Many played a version of “[Expletive] the Police” written by Baton Rouge-born rapper Boosie Badazz.

In Washington, several dozen people gathered outside the Justice Department headquarters on Friday, holding candles and quietly singing “We Shall Not Be Moved.”

“I feel like we as a people should not go out and kill off police officers or cops who are killing off our people, because then we’re becoming them,” said Jennifer Jones, a 20-year-old student at Davidson College in North Carolina, standing outside the White House. “I don’t want to become the oppressor. I don’t want to become the enemy. I don’t want to become the murderer.”

She added: “I want to be the person that can stand up and talk and fight for the right thing to happen.”

In Baltimore — the backdrop for riots last year following the death of Freddie Gray in police custody — about 300 people converged downtown Friday for a rally organized by the group Peoples Power Assembly, holding signs that read “Justice Now for Sterling and Castile.”

Protesters, escorted by police motorcycles, SUVs and officers on foot, headed through the city’s Inner Harbor, blocking traffic.

Among those marching in Baltimore was resident Tay Parker, 32, a black woman who worries about her three brothers being racially profiled, and now fears for the safety of her friend, a Maryland Transit Authority police officer.

“She’s judged for being in that uniform the same way people are judged for the color of their skin,” Parker said.

In New York, about 300 people gathered in Manhattan’s Union Square before splitting into small groups watched closely by police. One contingent marched across the Williamsburg Bridge into Brooklyn. Another moved through Grand Central Terminal. In upstate New York, police in Rochester arrested at least 74 people for disorderly conduct during a protest, the Associated Press reported.

Across California, protests ranged from marches in Los Angeles led by rappers Snoop Dogg and The Game, to a surge onto Interstate 880 in Oakland that closed 10 lanes of one of California’s busiest highways for more than two hours Friday. Some chanted: “No racist police.” Protesters returned to the roads Saturday, blocking a ramp to the Bay Bridge connecting San Francisco and Oakland.

In Denver’s Civic Center Park, dozens of people joined a sit-in that planned to stretch until Tuesday — representing one hour for every black person killed by police this year, organizers said. Supporters passed by with food, water and blankets.

Protestors blocking Airline Highway in front BRPD headquarters. More #AltonSterling coverage here: http://theadvocate.com/news/altonsterling

Posted by The Advocate (Baton Rouge, LA) on Friday, July 8, 2016

At least three people were arrested in Arizona on charges of pelting people with rocks, police said. Earlier, police used tear gas and pepper spray against protesters Friday trying to block traffic on Interstate 10, a key highway.

In Chicago, supporters of the Black Lives Matter movement led what it called a “die-in” outside Obama’s home to draw attention to police violence. A similar staged mass death was held on the sidewalk outside police headquarters in New Orleans.

Meanwhile, investigators looked into three shootings of police officers.

A man in Bristol, Tenn., shot a hotel clerk and then opened fire on a parkway, killing a motorist and shooting an officer in the leg before officers shot and wounded him. Authorities identified the shooter as Lakeem Keon Scott, 38.

“Preliminarily, the investigation reveals Scott may have targeted individuals and officers after being troubled by recent incidents involving African Americans and law enforcement officers in other parts of the country,” the Tennessee Bureau of Investigation said in a statement.

In Georgia, police said a man called 911 and then shot at the responding officer, leaving him wounded. And in the St. Louis suburb of Ballwin, Mo., a police officer was in critical condition after being shot during a traffic stop Friday morning. “It was clearly an ambush, an attack,” said St. Louis County Prosecuting Attorney Robert McCulloch. A suspect, Antonio Taylor, 25, of St. Louis, was arrested several miles from the shooting after a foot chase.

“I can’t continue to live in a world like this – it’s too painful,” said 19-year-old Taylor Quattlebaum during a Friday protest in Washington. “I can’t continue to cry every night before I go to sleep. It hurts too much.”

T. Rees Shapiro, Fenit Nirappil, Fred Barbash, Moriah Balingit, Aaron Davis, LaVendrick Smith, Victoria St. Martin, Perry Stein and Derek Hawkins contributed to this story.