Dallas: Dallas Police Chief David Brown has stepped into America's fierce gun rights debate, officially expressing what many have been thinking: that Texas state laws allowing civilians to carry firearms openly presents a challenge to law enforcement.

Texas is known for its gun culture, and state laws allow gun owners to carry their weapons in public. Some gun rights activists bring firearms to rallies as a political statement. Some did that at Thursday's march in Dallas.

A US Army reservist shot 12 police officers at that gathering, killing five, and injuring another seven officers and two civilians, in an apparent protest over police shootings of African-Americans. 

Dallas Police Chief David Brown answers questions on Monday. Photo: AP

"It is increasingly challenging when people have AR-15's slung over, and shootings occur in a crowd. And they begin running, and we don't know if they are a shooter or not," Brown said. "We don't know who the 'good guy' versus who the 'bad guy' is, if everybody starts shooting."

Seeing multiple people carrying rifles led police initially to believe they were under attack by multiple shooters.

A shooting incident in Michigan on Monday underscored the prevalence of gun violence in the United States and the danger faced by law enforcement, even as activists continue to protest fatal police shootings of two black men last week in Louisiana and Minnesota.

Dallas police chief David Brown, centre, in a candle light vigil at Dallas City Hall on Monday. Photo: AP

Two sheriff's bailiffs were shot dead at a courthouse in Michigan on Monday (local time), and the shooter was also killed.

By Monday evening, protesters were marching again in several American cities, including Chicago, Sacramento, California, and Atlanta, where local news footage showed a number of protesters being arrested after street demonstrations north of downtown.

President Barack Obama and others reiterated their calls for stricter guns laws after last month's massacre at a gay nightclub in Orlando, but many conservatives responded that such measures could infringe on the US Constitution's protection of the right to bear arms.

Demonstrators rally to protest recent police shootings of black men, in Sacramento, California, on Monday. Photo: AP

Brown did not explicitly call for gun control laws, but said: "I was asked, well, what's your opinion about guns? Well, ask the policymakers to do something and I'll give you an opinion."

"Do your job. We're doing ours. We're putting our lives on the line. Other aspects of government need to step up and help us," he added.

Rick Briscoe, legislative director of gun rights group Open Carry Texas, said Brown was "simply mistaken" in viewing armed civilians as a problem.

Killed by a robot: Police killer Xavier Johnson

"It is really simple to tell a good guy from a bad guy," Briscoe said. "If the police officer comes on the situation and he says: 'Police, put the gun down,' the good guy does. The bad guy probably continues doing what he was doing, or turns on the police officer."

During the Monday news conference, Brown also gave new details about his department's use of a bomb-carrying robot to kill the shooter Micah Johnson.

Police used a Northrop Grumman Corp Mark5A-1 robot, typically deployed to inspect potential bombs after concluding during an hours-long stand-off there was no safe way of taking Johnson into custody.

Open-carry activist Mark Hughes at the Dallas rally on Thursday. Police tweeted his photo and described him as a suspect as events unfolded. Photo: Dalls Police/AP

"They improvised this whole idea in about 15, 20 minutes," Brown said.

"I asked the question of how much [explosives] we were using, and I said ... 'Don't bring the building down'. But that was the extent of my guidance."

The incident is believed to have been the first time US police had killed a suspect that way, and some civil liberties activists said it created a troubling precedent. But Brown said that in the context of Thursday's events, "this wasn't an ethical dilemma for me".

Activists rally against police brutality in downtown Chicago on Monday. Photo: Chicago Tribune/AP

The attack came at the end of a demonstration decrying police shootings of two black men in Baton Rouge, Louisiana and near St. Paul, Minnesota. Those were the latest in a series of high-profile killings of black men by police in various US cities that have triggered protests.

In Dallas, a vigil was held for the slain officers on Monday evening.

In Chicago, images and footage on social media and local news stations showed about 500 protesters marching through downtown after holding a quiet sit-in in Millennium Park that spilled into the streets and a rally near City Hall.

Activists gather to rally against police brutality in Chicago. Photo: Chicago Tribune/AP

In Atlanta, local media footage showed a number of handcuffed protesters being loaded onto a police bus surrounded by armed officers and emergency vehicles with lights flashing. Television station WSB-TV reported that police started arresting demonstrators marching.

In Sacramento, about 300 people were marching peacefully on Monday evening. Earlier in the day, in an incident not linked to protests, Sacramento police said officers fatally shot a man carrying a knife after he charged at police.

Brown, who is black, urged people upset about the conduct of police to consider joining his police force.

Protesters against the recent police shootings of African-Americans in Atlanta on Monday. Photo: AP

"Get off that protest line and put an application in, and we'll put you in your neighbourhood, and we will help you resolve some of the problems you're protesting about," he added.

Reuters

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A protester is arrested during a march in Atlanta on Monday. Photo: AP

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