Derek Chauvin, the former Minneapolis police officer convicted in the death of George Floyd, was attacked in a prison in Arizona, Minnesota Attorney General Keith Ellison confirmed on Saturday.
The Associated Press earlier reported Chauvin had been stabbed and seriously injured on Friday.
"I am sad to hear that Derek Chauvin was the target of violence," Ellison said in an emailed statement.
"He was duly convicted of his crimes and, like any incarcerated individual, he should be able to serve his sentence without fear of retaliation or violence."
He did not give further details.
Chauvin is serving a 21-year federal sentence for violating Floyd's civil rights, as well as a concurrent 22-1/2 years for murder on his conviction in Minnesota state court.
The Federal Bureau of Prisons confirmed an unidentified inmate was assaulted at the Federal Correctional Institution in Tucson, Arizona. It said employees "initiated life-saving measures" for one individual, who was taken by emergency medical services to a hospital.
Floyd's death in 2020 unleashed protests worldwide against police brutality and racism after Chauvin, who is white, knelt on the neck of the handcuffed Black man for more than nine minutes in a murder caught on cellphone video.
(Reporting by David Ljunggren in Ottawa; Editing by Matthew Lewis)