Image copyright AP Image caption Brock Turner was seen by two witnesses sexually assaulting an unconscious woman

Legislators in California have closed a loophole in sexual assault cases, whereby more lenient sentences could be issued if the victim did not resist.

The change follows a high-profile sexual assault case in Stanford earlier this year.

In June, Brock Turner, 20, was sentenced to six months in jail for sexually assaulting an unconscious woman on a university campus.

The sentence was widely criticised for being overly lenient.

In California, the use of force in a sexual assault results in a mandatory prison sentence. In cases where no force is used - when the victim is unable to defend themselves - no mandatory sentence exists.

State assembly members voted unanimously to amend the law, and prevent the use of probation in such cases. The bill has been passed to Governor Jerry Brown for approval, but has not yet been signed into law.

Turner, a former top swimmer at Stanford University, was found guilty in March of three felony charges. Two witnesses said they had seen him sexually assaulting the woman, who was lying on the ground unconscious, on the university campus. Prosecutors wanted a sentence of six years in state prison.

Judge Aaron Persky, who handed out the sentence, expressed concern about the impact of prison on Turner. In his decision, he said positive character references and Turner's remorse and lack of previous criminal record were mitigating factors.

Brock Turner's father, Dan, also caused controversy during the case, saying his son should not have been jailed for "20 minutes of action".

The victim, referred to by the pseudonym Emily Doe, then released her victim impact statement publicly. It was read by millions, and openly praised by US Vice President Joe Biden.

Turner is expected to be released later this week after serving half his sentence, the Mercury News reports.

Santa Clara County District Attorney Jeff Rosen, who prosecuted Turner in the Stanford case, said legislators had helped protect "the next Emily Doe against the next Brock Turner".

"They not only read Emily Doe's now famous letter, but they clearly understood it as cry for change," he said in a statement.

Assembly member Evan Low said: "rape is rape, and rapists like Brock Turner shouldn't be let off with a slap on the wrist."

Death threats

The Stanford case was widely criticised, and became the focus for a campaign for tougher sentencing.

Judge Persky has faced death threats and online petitions demanding his removal following the case, and has now been assigned to the court's civil division at his own request, where he will no longer hear criminal cases.

The case has also been used as an example in other cases involving sexual assault on university campuses across the US.

In Massachusetts, high school athlete David Becker, 18, was sentenced earlier this month to probation on charges of indecent assault. His attorney, Thomas Rooke, told local media "The goal ... was not to impede this individual from graduating high school and to go onto the next step of his life."

"We all made mistakes when we were 17, 18, 19 years old, and we shouldn't be branded for life with a felony offence and branded a sex offender," he told the Mass Live news outlet.

Governor's Council member Michael Albano has called for a review of the sentence, which has been denied by the court.

Also this month, in Colorado, Austin James Wilkerson, 22, was sentenced to "work release" and probation for sexually assaulting a woman he had agreed to walk home after a party. The victim in that case also chose to publicly release her victim impact statement.