A US judge has set a trial date for four ex-police officers charged in connection with the murder of African American George Floyd for 8 March next, making clear he did not want the case to become a media circus with the presidential election looming.

Minneapolis Judge Peter Cahill warned the four, their attorneys and state officials not to play the case through the news, even as one lawyer pointed out that President Donald Trump had already weighed in.

"I would like to see pre-trial publicity not include statements from family from either side, police or elected officials" about guilt or innocence, or the merits of the case, he told a court in Hennepin County.

Derek Chauvin, the white officer filmed on 25 May pressing his knee into handcuffed Mr Floyd's neck for nearly eight minutes until he became unresponsive, faces second and third-degree murder charges.

Three others who were with Mr Chauvin when they detained the 46-year-old are charged with aiding and abetting a murder.

None of the four formally entered pleas.

Robert Paule, defending Tou Thao, one of the three charged with abetting the killing, said his client would plead not guilty, arguing that he adhered to police guidelines on use of force.

But Mr Paule also expressed concerns over prejudicial comments and actions by state and national officials that could impact the trial.

"In this case, we have comments made, I believe, by President Trump," as well as Minnesota's governor, the mayor of Minneapolis, the Minnesota attorney general and others, Mr Paule said.

He noted that Minnesota Attorney General Keith Ellison, whose office is leading the prosecution, and US Attorney Erica MacDonald met George Floyd's family in Houston, adding that the trip was leaked to the press.

Mr Paule said more publicity could lead to a push for a change of venue.

Eric Nelson, the lawyer for Mr Chauvin, said he might demand the judge legally order people involved to remain silent.

"If such public statements continue, I'll be seeking a gag order," Mr Nelson said.

The court case was held in the Public Safety Facility building in Minneapolis

Derek Chauvin, whose bail has been set at $1 million, appeared via video from the Oak Park Heights prison wearing an orange jumpsuit and a coronavirus mask.

The other defendants - Mr Thao, Alexander Kueng and Thomas Lane - appeared in person.

The four, who were fired from the Minneapolis police force one day after Mr Floyd's death, each face up to 40 years behind bars.

The bystander video of the death ignited protests and riots in cities across the United States and sparking a national debate on racism and police violence.

Mr Floyd was detained for the minor charge of attempting to use a counterfeit $20 bill, and while in handcuffs, two of the officers held him down on the street while Mr Chauvin pressed his knee to Floyd's neck and the fourth officer stood watch.

"I can't breathe," George Floyd said on several occasions before losing consciousness.

An independent autopsy later revealed that he died of suffocation due to the police officer's pressure on his neck and cited the cause of death as "homicide."

The original complaint said Mr Floyd was pinned by the neck for eight minutes and 46 seconds but this was revised down by 60 seconds last week.

The judge set the next procedural hearing for September, with all parties needing to assemble a massive amount of evidence.

Prosecutor Matthew Frank, an assistant Minnesota attorney general, said so far there are more than 8,000 individual pages of discovery and hundreds of audio recordings and photographs date-stamped in the case.