Baltimore's top prosecutor has announced criminal charges against all six police officers suspended after a black man suffered a fatal spinal injury in police custody, saying "no one is above the law".

Freddie Gray's arrest was illegal and his treatment in custody amounted to murder and manslaughter, Maryland's state attorney Marilyn Mosby said.

The announcement came after nearly two weeks of growing anger over Mr Gray's death, and only hours after Ms Mosby received the results of a police investigation.

"Mr Gray's death was a homicide," she declared.

Ms Mosby announced the stiffest charge - second-degree "depraved heart" murder - against the driver of the police van. Other officers face charges of involuntary manslaughter, assault and illegal arrest.

She said the knife officers accused Mr Gray of illegally carrying clipped inside his trouser pocket was in fact a legal knife, and there was no justification for his arrest.

Ms Mosby said she comes from five generations of police officers and that the charges against these six officers should in no way damage the relationship between police and prosecutors in Baltimore.

Her announcement came as the city braced itself for two more waves of protests today and tomorrow focused on the case.