Two inmates in separate California prisons were killed this week in attacks by other inmates, officials said. 

Sidney Kang, 31, died Thursday after he was attacked around 10 a.m. in a recreational yard at Kern Valley State Prison in Delano. He was treated for his injuries at the prison but died a short time later. 

Kang had been incarcerated since 2014 and was serving a 14-year sentence for assault with force likely to produce great bodily injury in Los Angeles County, officials said. He had a previous serious felony conviction and it was his second strike.

Authorities believed inmates Anthony Ramirez and Michael Caldera were behind the attack. The weapons used appeared to be made by inmates and the death was being investigated as a homicide. 

Ramirez, 40, was admitted to prison in 2008 from Los Angeles County and was serving a life sentence with a chance of parole. Two years ago, he received another 12 years for seriously assaulting someone in the Kern County prison and last year he received another two years for possessing or manufacturing a deadly weapon, officials said.

Caldera, 35, was sent to prison in 2010 from San Bernardino County and was serving 71 years and four months for several second-degree armed robbery convictions, authorities said.

Edgar Delgado, 39, died Tuesday evening after he was attacked by another inmate armed with a homemade weapon in a maximum security exercise yard at Salinas Valley State Prison in Soledad, prison officials said.

The assault was stopped by correctional officers using chemical agents, officials said. 

The death is being treated as a homicide and the name of the other inmate was not released. 

Va;ifornia prison deaths.

In this Aug. 16, 2016, file photo a condemned inmate is led out of his east block cell on death row at San Quentin State Prison, in San Quentin, Calif. Two inmates at other California correctional facilities died after being attacked this week, prison officials said (AP)

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Delgado was serving a sentence of life with the possibility of parole since 2008. He was convicted in Los Angeles County of attempted first-degree murder of a peace officer or firefighter with a firearm, shooting a firearm with gross negligence and possession of a firearm by an ex-felon.

The Associated Press contributed to this report.