A panel of federal judges on Monday ruled that California must release 55,000 state prisoners within three years to decongest the overcrowded prisons.

A federal appeals judge for the Ninth Circuit and two federal district judges said the tentative decision will ensure the constitutional rights of California's estimated 150,000 prisoners to adequate medical and mental health care.

They said decongesting the 33 adult prisons will also save the state from $803 million to $906 million in annual expenses.

"The evidence is compelling that there is no relief other than a prisoner-release order that will remedy the unconstitutional prison conditions," Nytimes.com quoted the panel as saying in its ruling on the class-action lawsuit accusing the state government of depriving prisoners of adequate health care.

Inadequate health care to prisoners is being blamed for the death of one inmate each month.

California Attorney General Jerry Brown said he will appeal the ruling.