Image copyright AP Image caption Bates told the judge he was "remorseful" for what happened

A US ex-police officer who killed an unarmed black man after apparently mistakenly using his gun instead of his Taser has been sentenced to four years in prison in the US state of Oklahoma.

Robert Bates, 74, has been given the maximum sentence recommended by jurors for second-degree manslaughter.

He killed Eric Harris, 44, in a sting operation over gun sales in Tulsa in April 2015. The victim's family said they did not think race was a factor.

Bates' lawyer said he would appeal.

The incident was captured on video and showed Mr Harris being chased and brought to the ground before he was shot.

A gunshot is heard and a man says, "Oh, I shot him. I'm sorry."

Mr Harris is heard calling out "He shot me, oh my God!" He later died in hospital.

Image copyright AP Image caption Police accused Mr Harris (left) of illegal gun sales

At the time of the shooting, Bates had been a reserve deputy in Tulsa County Sheriff's office, a volunteer position, since 2008.

He was also chief executive of an insurance firm and a major donor to the Sheriff's office.

Media playback is unsupported on your device Media caption A clip from the video released by Tulsa police

Judge Bill Musseman said the prison sentence was a "legitimate and moral consequence" of Bates' actions.

The accused, wearing orange jail clothing with his hands shackled, said in court: "I'm very remorseful for what happened."

A jury last month had found him guilty and recommended the four-year sentence.

The case provoked an outcry as it followed other incidents where a white officer killed a black man, raising concerns of racial discrimination and lack of police training.