Protesters confront the police during a massive street protest over the killing of George Floyd in Los Angeles, the United States, May 30, 2020. (Xinhua)

Three Minneapolis policemen were charged Wednesday for their role in the killing of a handcuffed black man that ignited nationwide protests, while more serious charges were filed against the officer primarily responsible.

Minnesota prosecutors had announced a third-degree murder indictment Friday against 44-year-old Derek Chauvin - the white officer filmed kneeling on the neck of George Floyd for nearly nine minutes while he pleads: "I can't breathe."

But they said they were increasing the charge, roughly akin to manslaughter, to second-degree murder, which does not involve premeditation but carries stiffer penalties.

"I believe the evidence available to us now supports the stronger charge of second-degree murder," Minnesota Attorney General Keith Ellison said.

Chauvin's three colleagues, at the scene of Floyd's May 25 arrest for allegedly seeking to buy cigarettes with a counterfeit bill, are accused of being complicit in the killing.

Tou Thao, 34, J. Alexander Kueng, 26, and Thomas Lane, 37, were charged with aiding and abetting second-degree murder.

The arrest of all of the officers involved has been a persistent demand of protesters who have taken to the streets of dozens of US cities for the past nine days to condemn police brutality and demand racial justice.

Tens of thousands of people defied curfews in several US cities overnight to voice anger over 46-year-old Floyd's death but the protests were largely peaceful and did not feature the looting or clashes with police of previous days.

Floyd's family, in a statement, called the arrests a "bittersweet moment" and a "significant step forward on the road to justice."

"These officers knew they could act with impunity, given the Minneapolis Police Department's widespread and prolonged pattern and practice of violating people's constitutional rights," his family said.

"We are deeply grateful for the outpouring of support by Americans in cities across the country, and we urge them to raise their voices for change in peaceful ways."

Former US president Barack Obama on Wednesday applauded the "profound" protests demanding racial justice and said demonstrations over last week's killing of a black man in police custody could spark nationwide reforms.

In his first video comments since George Floyd's death on May 25 in Minneapolis triggering unrest across the country, President Donald Trump's predecessor also urged state and local authorities to review their policies on the use of force.

Obama directed his comments at young black men and women who he says have often witnessed or experienced too much violence.

"Too often some of that violence has come from folks who were supposed to be serving and protecting you," Obama said in a webcast with activists.

AFP