KENOSHA, Wisconsin (REUTERS) - Wisconsin prosecutors on Tuesday (Jan 5) cleared a white police officer in the Aug 23 shooting of Black man Jacob Blake from behind in the presence of his young children, leaving him paralyzed and triggering deadly protests that inflamed racial tensions.

Kenosha County District Attorney Michael Graveley found police officer Rusten Sheskey acted in self-defence while shooting Blake seven times at close range, saying Blake was armed with a knife and had resisted arrest, withstanding multiple Taser shots.

The decision against prosecuting Sheskey or the two other officers on the scene could incite more demonstrations, which have frequently broken out in the United States in recent years after police have been cleared of wrongdoing in shootings of African Americans.

Lawyers for Blake said the officer should have been charged with attempted homicide and called on people to advocate for racial justice and police reform.

After the sun set and the temperature dipped below freezing, Kenosha's business districts were largely empty with many storefronts boarded up in anticipation of violence.

"People are definitely on edge still," said life-long Kenoshian Jon Zamora, 30, as he boarded up a storefront in Kenosha, a city of 100,000 people between Milwaukee and Chicago.

Wisconsin Governor Tony Evers authorised the Wisconsin National Guard to support local law enforcement.

Investigators previously said a knife was found at the scene, but a weapon was not easily visible in Blake's hand on the video of the shooting that went viral on social media. Nor did the video show previous attempts to detain Blake, who was wanted on a felony arrest warrant, as police were told before arriving on the scene, Graveley said.

Blake refused police commands to drop the knife, which Graveley said gave Sheskey the right to self-defence.

"It is absolutely incontrovertible that Jacob Blake was armed with a knife during this encounter," Graveley said, adding that Blake admitted several times to investigators he had the knife.

Seven shots

Sheskey fired seven times until Blake dropped the knife, a justified number and in accordance with police training, said former Madison Police Chief Noble Wray, who had been named by the Wisconsin Department of Justice to review the investigation.

Wray, who is Black, said he recognised the history of racism in the criminal justice system but the decision not to prosecute was grounded in the facts.

"It has been a stressful endeavor to be involved in policing for 37 years and to be an African American male. And I feel it in the worst way. That's why this is so difficult, but I was not going to step back from it," Wray said.

Graveley called the incident a tragedy for all those involved, especially Blake, who was paralysed from the waist down. Blake's lawyers said they are considering a civil lawsuit against Sheskey.

The shooting took place while passions were still inflamed over the May 25 death of George Floyd, a Black man, after a white Minneapolis police officer knelt on his neck. Thousands took the streets in "Black Lives Matter" anti-racism protests in the United States and around the world following Floyd's death despite the coronavirus pandemic.

"We must broaden the fight for justice on behalf of Jacob Blake and the countless other Black victims of racial injustice and police brutality," Blake's lead attorney Ben Crump, who has represented other African Americans in high-profile civil rights cases, said on Twitter on Tuesday.

B'Ivory LaMarr, another lawyer for the Blake family, told reporters the officer failed to reduce the tension from the situation and disputed the police account of Blake's threatening behaviour.

"The video made it clear that Jacob... never raised a knife," LaMarr said.

The Sheskey shooting of Blake attracted a mix of civil rights demonstrators, anarchists and right-wing militias to Kenosha.

At the height of those protests, teenager Kyle Rittenhouse opened fire with a Smith & Wesson M&P 15 rifle, killing two men and wounding another. Rittenhouse, now 18, was charged with first-degree reckless homicide and five other criminal counts.

Earlier on Tuesday, Rittenhouse pleaded not guilty to all counts in an appearance by video in Kenosha County Circuit Court.