MINNEAPOLIS (AFP) - Derek Chauvin, the white former Minneapolis policeman convicted of murdering African-American George Floyd, pleaded guilty on Wednesday (Dec 15) to violating Mr Floyd's civil rights - his first acknowledgement of criminal wrongdoing in the case.

Chauvin pleaded guilty in the courthouse in St Paul, Minnesota, to federal charges of use of excessive force for holding his knee to Mr Floyd's neck for nearly 10 minutes on May 25 last year until Mr Floyd died.

Mr Floyd's death, which was filmed by a bystander on a mobile phone, set off months of Black Lives Matter demonstrations throughout the country over police abuse of black people.

Chauvin was convicted in a state trial of murder in June and was sentenced to 22½ years in prison.

But he has not admitted guilt to the murder charges and is appealing that conviction.

Chauvin had originally pleaded innocent in the federal rights case. But the judge told him that if he had not changed that to guilty, he faced possible life imprisonment, according to local station WCCO TV.

After he reversed his plea, federal prosecutors said Chauvin could be sentenced to between 20 and 25 years, served concurrently with and beyond the sentence in the murder conviction.

That ensures the 45-year-old former Minneapolis policeman will spend years in prison, whatever happens with his appeal on the murder charge.

In May last year, the 19-year veteran of the Minneapolis police force was seen on video kneeling on Mr Floyd's neck as he lay face down and handcuffed on the ground saying repeatedly "I can't breathe".

That became the mantra of subsequent protests, which gained force as other unpunished cases of mistreatment or killings of black people by police came to light.

Three other now former officers were at the scene of Mr Floyd's death and are to be tried separately in the state's murder case: Tou Thao, Alexander Kueng and Thomas Lane.

The three were also charged in the federal rights case and have pleaded not guilty.

Civil rights lawyer Ben Crump, who has represented Mr Floyd's family, called the resolution of the federal case a historic day.

"Before the tragic and needless death of George Floyd, there was little expectation that a white police officer would ever be held accountable for murdering a black man," he said.

"When Derek Chauvin was held to account, the jury - and people across the country - finally said enough was enough."

Mr Floyd's brother, Mr Philonise Floyd, said outside the courthouse that his family moves ahead but "can never heal". He said people frequently tell him that his brother's death changed the world.

"I'm happy that more people are willing to talk about what's going on across America," he said.

However, he added: "I cry about it all the time. We can never have George back."