LOS ANGELES (AFP) - A US jury failed again on Thursday to agree on whether to sentence Jodi Arias to death for the grisly killing of her boyfriend in 2008, effectively sparing her the death penalty.

Judge Sherry Stephens declared a second mistrial in Phoenix, Arizona, the latest development in a case which has gripped America.

The judge set a sentencing date of April 13, when Arias can be sentenced to life in prison with or without parole.

Arias had been on trial since January 2013, accused of murdering Travis Alexander, 30, in a frenzied attack in June 2008 in which he was stabbed 27 times, shot in the head and had his throat slit.

A first jury failed in May 2013 to reach a verdict on the death penalty, leading to a retrial on the sentencing phase which climaxed in Thursday's hung jury.

At her trial Arias claimed she was acting in self-defence, but a jury found her guilty of premeditated murder.

Arias had said she would prefer death to life in prison, and repeated that in a television interview shortly after her 2013 conviction.

But she later begged the jury to spare her life, listing the good things she could achieve behind bars, including starting a book club and donating hair to make wigs for cancer patients.