Craig Harvey, a spokesman for the Los Angeles County coroner's office, told reporter the cause of death will not be known until after further testing is completed, which will likely take four to six weeks.
"The cause of death has been deferred, which means that the medical examiner has ordered additional testing such as toxicology and other studies," Harvey said.
"There was no indication of any external trauma or indication of foul play for Mr. Michael Jackson," he said.
Harvey said investigators have determined Jackson was "taking some prescription medication" but he said he could not comment on "any specific drugs that Mr. Jackson may have been prescribed or used."
Jackson was 50 when he died Thursday after being rushed, in apparent cardiac arrest, from his home to UCLA Medical Center, where efforts to resuscitate him failed.
Los Angeles police said late Friday they had been able to reach Dr. Conrad Murray, who was with Jackson when he collapsed, the Los Angeles Times reported. Detectives did not say when they would interview him.
Murray's car was impounded Friday to be searched for medications. He talked to police Thursday.
The Jackson family's longtime lawyer said prescription drug abuse may have been what killed him.
"I don't know what caused Michael's death, and I don't want to speculate as to what the causes are," attorney Brian Oxmon told Usmagazine.com. "I only know that I warned them there was the misuse of prescription medications by people who were enabling him; his handlers, folks who should never have been permitted to allow him to use those medications in the manner I observed. So, is that the cause of it? I don't know. People die from various and sundry causes -- they have congenital malformations of the heart, they have difficulty with various infections. I don't know what Michael Jackson's death is a result of."
Oxmon added Jackson "had no particular health concerns except that he had broken his leg many years ago, and it hurt him."
"He had cracked a vertebrae in his back and he took painkillers to try to ease the pain," he told Usmagazine.com. "And now we find ourselves here. I don't know if the two are connected. I had warned that the misuse of medications would result in this, and I am heartbroken that we are here."
Marlon Jackson, one of Michael Jackson's siblings, told CNN he learned of his brother's death through his manager, Frank Dileo.
"Frank told me that Michael last night was complaining about not feeling well. He called to tell him he wasn't feeling well," Marlon Jackson said Thursday. "Michael's doctor went over to see him, and Frank said, 'Marlon, from last night to this morning, I don't know what happened.' When they got to him this morning, he wasn't breathing."