The governor of the north-central US state of Wisconsin activated the state's National Guard on Sunday after protests of a police shooting turned violent and businesses and cars were torched overnight in the city of Milwaukee.
Officials were calling for calm in the hopes that violence would not resume overnight after six businesses were torched and looted a night earlier. Seven police vehicles were also damaged.
"Last night was unlike anything I have seen in my adult life in this city and I hope I never see it again," Mayor Tom Barrett said, calling on parents to keep their children away from the area on Sunday.
The violence broke out after a police officer shot and killed a man on Saturday amid heightened tensions between the minority African American community and police.
There was no question that the man who was shot, identified as 23-year-old Sylville Smith, had a gun in his hand as he was pursued by a police officer, Barrett said. Smith had an extensive criminal record, officials said.
An image from the police officer's body camera "demonstrates without question that he had a gun in his hand," Barrett told a press conference.
Seventeen people were arrested, while four police officers were wounded by flying debris, police chief Edward Flynn said.
The National Guard, which serves as the reserve force of the US military but is frequently used by state officials in disaster response, was to assist local police at their request, Governor Scott Walker said in a statement.
Some 120 National Guard troops would be in the city, but would not be used unless the police chief makes a specific request, Barrett said.
Residents had meanwhile gathered Sunday to assist with clean-up in what Walker called an "act of selfless caring."
"I join Milwaukee's leaders and citizens in calling for continued peace and prayer," he said.
At least 200 people were involved in the disturbances, police official James Harpole said at an earlier press conference.
Khalif Rainey, a local alderman, said that the shooting and violence pointed to the mounting tension between Milwaukee's black community and police.
"No one can deny the fact that there's problems, racial problems, here in Milwaukee, Wisconsin, that have to be closely, not examined, but rectified. Rectify this immediately," said Rainey, who represents the area where the man was shot, according to the Journal Sentinel.
The shooting comes amid ongoing tensions between minority communities and police that have resulted in nationwide protests in recent years.
The police officer involved in the shooting was also black, Flynn said.