US protests over the death of George Floyd in custody have dwindled overnight after prosecutors levelled new charges against four Minneapolis police officers implicated in the killing.
Huge crowds have defied curfews and taken to the streets of cities across the country for nine nights in sometimes violent protests that prompted President Donald Trump to threaten to send in the military.
Floyd, a 46-year-old African American, died after a white policeman pinned his neck under his knee for nearly nine minutes in Minneapolis on May 25, propelling the issue of racial justice to the top of the political agenda five months before the presidential election on November 3.
Former Defence Secretary Jim Mattis denounced a militarisation of the response to civil unrest. Current Defence Secretary Mark Esper also said he did not back the use of troops to patrol the country.
"Donald Trump is the first president in my lifetime who does not try to unite the American people -- does not even pretend to try," Mattis, who resigned as defence secretary in 2018, wrote in The Atlantic.
"Instead he tries to divide us. We are witnessing the consequences of three years of this deliberate effort."
The chairman of the Joint Chiefs of Staff, Army General Mark Milley, issued a message reminding the armed forces of their oath to uphold the Constitution, which gives Americans the right to "freedom of speech and peaceful assembly."
Thousands of demonstrators massed near the White House lit up their mobile phone flashlights and sang along to the 1970s soul tune "Lean on Me," before resuming anti-police chants.
Several major cities scaled back or lifted curfews imposed for the past few days.
In New York City's Brooklyn borough, police in riot gear charged into a crowd of about 1000 protesters defying a local curfew, albeit peacefully, and clubbed demonstrators and journalists as they scurried for cover in heavy rain.
A man armed with a knife stabbed and wounded a Brooklyn policeman in the neck and two officers who ran to his rescue were wounded before they shot the attacker multiple times, police said. All four were taken to the hospital.
Derek Chauvin, 44, arrested on charges of third-degree murder and manslaughter, was also charged with second-degree murder.
The added charge, defined under Minnesota law as unintentionally causing another person's death in the commission of a felony offence, can carry a sentence of up to 40 years.
Chauvin was the white officer seen in video footage kneeling on Floyd's neck as Floyd gasped for air and repeatedly groaned, "Please, I can't breathe."
The video immediately went viral, igniting the nationwide protest and civil strife. Demonstrators have also taken to the streets overseas, from Britain to Australia.
Floyd, whom police suspected of trying to pass a counterfeit bill to pay for cigarettes, was pronounced dead at a hospital shortly after the encounter.
The official cause of death, according to the full 20-page autopsy report made public on Wednesday was cardiopulmonary arrest while Floyd was being restrained by police.
The autopsy also cited "complicating law enforcement subdual, restraint and neck compression."
The manner of death was listed as homicide.
Three fellow officers fired from the Minneapolis police department along with Chauvin the next day were charged on Wednesday - each with aiding and abetting both second-degree murder and manslaughter.
The three men - Thomas Lane, J. Alexander Kueng and Tou Thao - have also been taken into custody. Aiding and abetting second-degree murder carries the same maximum punishment as the underlying offense - 40 years in prison.
Memorial services, which will stretch across six days and three states, were due to begin on Thursday in Minneapolis, the lawyer for Floyd's family told media.
A funeral is planned for Tuesday with private services at an undisclosed location.
Australian Associated Press
Sign up for our newsletter to stay up to date.