KENOSHA, WISCONSIN • Investigators of a shooting in Wisconsin by a white police officer that left a black man, Mr Jacob Blake, paralysed found a knife belonging to Mr Blake at the scene of the confrontation, the state attorney-general said on Wednesday.

The shooting sparked three nights of civil unrest that has included a wave of arson, widespread vandalism and a separate shooting that claimed two lives in Kenosha, a city of about 100,000 residents on Lake Michigan, 60km south of Milwaukee.

Facebook also said it removed a page for the Kenosha Guard, a group which had posted a "call to arms" in Kenosha, saying the page violated its policy against "militia organisations".

In the first official details of Sunday's shooting released by the Wisconsin Justice Department, which is probing the incident, Attorney-General Josh Kaul said the knife was recovered from the driver-side front floorboard of the car that Mr Blake was leaning into when he was shot in the back.

Mr Kaul also told a news conference that during the course of the investigation, Mr Blake had "admitted that he had a knife in his possession".

Mr Blake's lawyer responded in a statement that his client posed no threat to the police and disputed that he was in possession of a knife.

Mr Kaul did not describe the knife or say whether it had anything to do with why the officer - a seven-year veteran of the Kenosha Police Department identified as Mr Rusten Sheskey - had opened fire on Mr Blake.

Mr Kaul's briefing came shortly before the United States Justice Department announced it had opened a federal civil rights inquiry into the shooting, to be conducted by the Federal Bureau of Investigation in cooperation with the Wisconsin authorities.

In a separate development hours earlier, a teenager was arrested and charged with shooting three people, two of whom died, during Tuesday night's protests in Kenosha.

Video footage from that incident shows a white gunman, armed with an assault-style rifle, firing at protesters who try to subdue him, and then calmly walking away from the scene - hands in the air and his rifle hanging in front of him - as several police vehicles drive by without stopping him.

Wisconsin Lieutenant-Governor Mandela Barnes told MSNBC that the suspect - later identified as Kyle Rittenhouse, 17, from Antioch, Illinois - was apparently a militia group member who "decided to be a vigilante and take the law into his own hands and mow down innocent protesters".

REUTERS