US attorney general Merrick Garland is expected to announce the Justice Department is opening a sweeping investigation into policing practices in Minneapolis after the guilty verdict in George Floyd’s death, a source has said.

The announcement is expected a day after former officer Derek Chauvin was found guilty of murder and manslaughter in Mr Floyd’s death last May, setting off a wave of relief but also sadness across the country.

The black man’s death prompted months of mass protests against policing in the US.

The Justice Department is already investigating whether the officers involved violated Mr Floyd’s civil rights.

The investigation is known as a “pattern or practice” and will be a more sweeping probe of the entire department and may result in major changes to policing there, the official said.

It will examine tactics used by police and whether the department engages in discriminatory practices and will also look at the department’s handling of misconduct allegations, among other things, the source said.

President Joe Biden has promised his administration will not rest following the jury’s verdict in the case, saying much more needs to be done.

“‘I can’t breathe.’ Those were George Floyd’s last words,” Mr Biden said. “We can’t let those words die with him. We have to keep hearing those words. We must not turn away. We can’t turn away.”

The Justice Department had considered opening a pattern or practice investigation into the police department soon after Mr Floyd’s death, but then attorney general Bill Barr was hesitant to do so at the time, fearing it could cause further divisions in law enforcement amid widespread protests and civil unrest, sources told the Associated Press.