At least 40 cities in the US including Washington DC have imposed curfews on Sunday in response to the continuing violent protests against the death of African-American man George Floyd.

The unarmed man died after Derek Chauvin, a white police officer, held him down with a knee on his neck though he repeatedly pleaded "I can't breathe." Chauvin was arrested and charged with three-degree murder and manslaughter earlier on Friday.

Cities having curfews:

• Arizona: Weeklong statewide curfew
• California: Los Angeles County, San Francisco, Beverly Hills, Santa Monica, West Hollywood, San Jose
• Colorado: Denver
• District of Columbia
• Florida: Miami, Orange County, Jacksonville, Orlando
• Georgia: Atlanta
• Illinois: Chicago
• Indiana: Indianapolis
• Kentucky: Louisville
• Michigan: Detroit
• Minnesota: Minneapolis, St. Paul
• Missouri: Kansas City
• New Jersey: Atlantic City
• New York: Rochester
• Ohio: Cincinnati, Cleveland, Columbus, Dayton, Toledo
• Oregon: Portland, Eugene
• Pennsylvania: Philadelphia, Pittsburgh
• South Carolina: Charleston, Columbia, Myrtle Beach
• Tennessee: Nashville
• Texas: Dallas, San Antonio
• Utah: Salt Lake City
• Virginia: Richmond
• Washington: Seattle
• Wisconsin: Milwaukee, Madison

"Today, about 5,000 National Guard soldiers and airmen are supporting our local and state partners responding to civil unrest in 15 states and DC [District of Columbia]. Thousands more stand ready if needed," Chief of the National Guard Bureau Gen. Joseph Lengyel said on Sunday.

Earlier, US National security adviser Robert O'Brien denied that systemic racism is present across the American police forces.