MINNEAPOLIS, USA - Demonstrations continued across the United States on Sunday as the nation braced for another gruelling night of unrest over police shootings and the death of George Floyd, amid growing concern that aggressive law enforcement tactics intended to impose order were instead inflaming tensions.

Videos showed police officers in recent nights using batons, tear gas, pepper spray and rubber bullets on protesters, bystanders and journalists, often without warning or seemingly unprovoked. The footage, which has been shared widely online, highlighted the very complaints over police behaviour that have drawn protests in at least 75 cities across the United States.

In Salt Lake City, officers in riot gear shoved a man with a cane to the ground.

In Brooklyn, two police S.U.V.s plowed into a crowd of protesters.

In Atlanta, police officers enforcing a curfew stopped two college students in a car, fired Tasers on them and dragged them out of the vehicle.

Videos showed officers using batons, tear gas, pepper spray and rubber bullets on protesters and bystanders.

Mayors and police chiefs spent the day explaining, defending and promising full investigations into the actions of officers seen on the disturbing videos.

And in Minneapolis, where there have been six consecutive nights of protests and clashes, a video appeared to show officers yelling at people on their porches to get inside and then firing paint canisters at them. “Light them up,” one officer said.

As crowds began gathering again in cities on Sunday, President Trump resisted calls to address the tensions roiling the country. Instead he used Twitter to criticize local Democratic leaders for not doing more to control the protests.

Not all protests have erupted in violence, with some police forces showing a more positive relationship with their communities. In Petersburg, Va., Chief Kenneth Miller and a handful of police officers appeared alongside protesters to show solidarity. In Newark, a city where half the population is black, protests were angry but nonviolent.

And in Oklahoma City on Sunday, as a crowd of marchers seemed to grow tense, officers with the sheriff’s department’s tactical team took a knee in a pose popularized by the former N.F.L. quarterback Colin Kaepernick. The protesters cheered.

In other places, there was open hostility, with chaotic scenes and constant videotaping among protesters increasing the scrutiny on the tactics used by the police.

In Minneapolis, businesses have been burned and looted and the National Guard has been called in to help restore order. But a member of the City Council, Jeremiah Ellison, summed up the situation this way: The police started it.

Two crises convulse the United States: A pandemic and police violence.

Emotions were already raw over the toll of a pandemic that has killed more than 100,000 people across the country and cost millions of jobs.

President Trump spent Sunday out of sight, berating opponents on Twitter, even as some of his campaign advisers were recommending that he deliver a televised address to an anxious nation.