An inmate was found Friday unresponsive in his Mille Lacs County jail cell and died, officials said.

Sheriff Kyle Burton identified the inmate as Robert James Sam, 57, of Onamia, Minn.

Emergency medical personnel and jail staff provided immediate aid to Sam, who was taken by ambulance to a hospital but could not be revived, the sheriff said.

Sam had turned himself in two days earlier to satisfy an outstanding warrant for his arrest, Burton said.

The cause of death is pending the results of toxicology tests, the sheriff said.

"We are working to conduct a comprehensive investigation into the circumstances surrounding this unfortunate event," a statement from Burton read. "We ask for your patience and understanding as we continue to gather facts and work through the investigative process."