"Black Lives Matter" activist DeRay Mckesson and 98 other people were arrested and detained Sunday during a street demonstration in Baton Rouge, the Louisiana city where videos of police officers fatally shooting a restrained street vendor sparked widespread condemnation.

US President Barack Obama has called for police reform and the US Justice Department is investigating both the shooting in Louisiana and another in Minnesota.

Anger and dismay continue to smolder at the street level. Hundreds of people turned out in the state capital to march and chant anti-violence slogans as riot police moved in and aggressively jostled protesters, witnesses said.

Prominent activist detained for 'blocking traffic'

"The police in Baton Rouge have been truly awful tonight," Mckesson said on a video live-streamed to social media. "They have provoked people. They chase people just for kicks. The police have been violent tonight. The protesters have not."

Moments later, someone shouts, "This is the police, you're under arrest! Don't fight me! Don't fight me!" Mckesson responds: "I'm under arrest, y'all!" before the camera falls and the transmission ends.

Meanwhile, in Minnesota, where the aftermath of a police killing of a black motorist during a traffic stop was live-streamed on social media, riot police fired smoke bombs to clear more than 200 demonstrators blocking a major highway.

Mike Martin, who wore a guitar on his back and said he was trying to promote peace, was pepper-sprayed by an officer on a pedestrian bridge overlooking the highway. He said he was trying to move the crowd along and keep things orderly.

"I guess I wasn't moving fast enough for him," said Martin, who said the officer was two meters (six feet) away when he sprayed him without warning. "He just got it out and bam, I saw a cloud. It's burning pretty bad."

Local TV and radio stations reported that news reporters have been detained and also charged for obstructing the highway.

Tensions between black citizens and police have risen markedly over the past week amid police shootings that have in recent years have been captured on video and shared widely on social media.

The situation was further inflamed when 25-year-old Micah Johnson, a black US army veteran, opened fire on Dallas police officers with a high-powered rifle, killing five before being killed by police. Authorities in Dallas said that the man's motive was apparently retaliation for police killings of black men and that he had been disenchanted with the peaceful Black Lives Matter movement.

New details from Dallas

New details released about Johnson on Sunday have cast light on a vague picture of the Afghanistan war veteran who apparently supported black militant organizations, some classified as hate groups.

Police said Johnson's military training apparently benefited him during the shooting, as he effectively triangulated police and shot at them with his high-caliber rifle. While holed up in a parking garage in a standoff with police officers, he had reportedly taunted negotiators and scrawled on a wall in his own blood before he was ultimately killed.

A search of his Dallas-area home turned up bomb-making materials and materials leading authorities to declare he had been planning a large attack long beforehand, and that the two police killings were a trigger that set him off.

jar/sms (AP, AFP)