Sirhan B. Sirhan, who is serving a life sentence for the 1968 assassination of Senator Robert F. Kennedy, was in stable condition at a Southern California hospital on Friday night after reports that he had been stabbed in prison by another inmate, the state prison system said.

The state Department of Corrections and Rehabilitation would not confirm that Mr. Sirhan, who is now 75, had been attacked, citing a state law shielding the names of crime victims.

But it did confirm that an inmate had been stabbed at 2:21 p.m. at the Richard J. Donovan Correctional Facility in San Diego, where Mr. Sirhan is serving his sentence, and that no other inmates had been attacked on Friday.

Officials would not say what had prompted the attack, which was first reported by TMZ.

Mr. Sirhan has been denied parole 15 times. His next parole hearing is in 2021.