Image caption Mehserle, shown in 2009, said he thought Grant was reaching for a gun

A white ex-police officer has been sentenced to the minimum possible jail term of two years for shooting dead an unarmed black man in California.

Johannes Mehserle was convicted in July of involuntary manslaughter in what was seen as one of the most racially divisive US trials in recent years.

He shot Oscar Grant in the back on the subway on 1 January 2009, while attempting to subdue him after a fight.

Mehserle, 28, had faced a possible 14-year maximum term.

The case has previously sparked several incidents of racial unrest, and police in the city of Oakland - where the shooting occurred - were on standby on Friday night after a sentence some perceived as too light.

The Associated Press reported that when Wanda Johnson, Grant's mother, heard Superior Court Judge Robert Perry issue the two-year sentence she burst out of the courtroom saying, "He got nothing! He got nothing!"

Johnson family attorney John Burris said the sentence was insufficient, adding: "What you take from that is that Oscar Grant's life was not worth very much."

But Justice Perry said there was overwhelming evidence the shooting, on New Year's Day 2009, had been accidental.

'Gun mistaken for Taser'

On the night of the shooting, police officers identified Grant, a 22-year-old African-American man, as a participant in a fight on a train.

Mehserle and another officer attempted to subdue him, and Mehserle testified that he saw Grant digging in his pocket and feared he had a gun.

He told his trial he had intended to use an electric Taser weapon but mistakenly pulled and fired his duty handgun instead.

The incident, recorded by onlookers on their mobile phones, sparked a period of violence, with protesters clashing with police and rioters setting cars ablaze and damaging businesses.

The case was moved to Los Angeles, because of tensions in Oakland.

After a jury in July rejected charges of murder or voluntary manslaughter a crowd of about 500 people marched in protest in Oakland at the outcome of the trial.

Later sporadic violence broke out in the town with rioters damaging shops, cars and setting fires.