A lawyer for the family of George Floyd, whose death sparked unrest across the US, has accused a police officer of “premeditated murder”.

Minneapolis policeman Derek Chauvin has been charged with third-degree murder, but lawyer Benjamin Crump told CBS news it was a case of first-degree murder.

“We think that he had intent… almost nine minutes he kept his knee in a man’s neck that was begging and pleading for breath,” he said.

Several US cities have imposed curfews.

The Floyd case has reignited US anger over police killings of black Americans. It follows the high-profile cases of Michael Brown in Ferguson, Eric Garner in New York and others that have driven the Black Lives Matter movement.