The head of police in Tulsa in the US state of Oklahoma says a black man shot dead by officers on Friday was unarmed.

Authorities are investigating the death of Terence Crutcher, 40, who had his hands in the air when he was shot next to his car, relatives say.

Tulsa Police Chief Chuck Jordan said “there was no gun on the suspect or in the suspect’s vehicle” and promised justice would be achieved.

Police say they will release a dash cam recording of the shooting.

Officers came across Mr Crutcher’s stalled vehicle while they were en route to another call, reports say.

Disturbing footage from a police helicopter of the moment Mr Crutcher was shot appears to back up his family’s assertion that his hands were in the air at all times.

He was first tasered and then shot. He died later in hospital, police said.

Mr Crutcher’s twin sister Tiffany called for protests over his death to be peaceful, and demanded criminal charges be filed against the officer who fatally shot him.

A series of high-profile incidents involving African-Americans dying at the hands of police have led to demonstrations across the US.