A fan puts a candle by a portrait of pop star Michael Jackson at the U.S. Embassy in Moscow on Friday. (Sergei Karpukhi/Reuters)

More testing has been ordered to determine the cause of pop icon Michael Jackson's death but an autopsy has revealed that there was no indication of external trauma or foul play to the body.

Craig Harvey, chief coroner of Los Angeles County, said following Friday's three-hour post mortem that the determination of the cause of death has been deferred for additional testing, such as toxicology, neuropathology and pulmonary testing, which could take four to six weeks to complete.

He said Jackson was taking some unspecified prescription medications but wouldn't elaborate. Harvey said the police department has requested a security hold on the investigation, meaning he was limited in the amount of information he can release.

Early Friday afternoon, the Los Angeles fire department released the 911 call for help made the previous day from Jackson's home in the Holmby Hills area of Los Angeles.

An unidentified caller is heard repeatedly urging the paramedics to hurry, saying that a 50-year-old victim wasn't responding to efforts by a personal doctor to revive him.

"I need an ambulance as soon as possible, sir," the caller said. "We have a gentlemen here that needs help and he's not breathing yet. He's not breathing and we need to … we're trying to pump him, but he's not, he's not."

Ed Winter, assistant chief coroner for Los Angeles County, discusses Jackson's autopsy with reporters in Los Angeles on Friday. (Phil McCarten/Reuters)

Earlier, Ed Winter, assistant chief coroner for Los Angeles County, refused to comment on reports that Jackson had been given an injection of the drug Demerol, used to treat pain, prior to his death.

There have also been reports that Jackson was addicted to the painkiller OxyContin.

"We're treating this case as we do all cases of deaths that happen in the county of Los Angeles," he said. "A lot of the tests have to run its course. They are time-consuming."

Police were preparing to question Conrad Murray, a cardiologist and Jackson's personal physician for three years, who was reportedly performing CPR on Jackson when paramedics arrived at his home Thursday.

Police said they towed Murray's BMW from the entertainer's home because it may contain medications or other evidence that may assist the coroner in determining the cause of death.

Detectives spoke with Murray after Jackson's death.

"We do not consider him to be unco-operative at this time," police Deputy Chief Charlie Beck said. "We think that he will assist us in coming to the truth of the facts in this case."

Believed to have suffered cardiac arrest

Michael Jackson may have been taking too many prescription drugs, his lawyer has said. (Lennox McLendon/Associated Press)

Jackson was pronounced dead at UCLA Medical Center Thursday afternoon, after apparently suffering cardiac arrest at his home.

Leslie Saxon, chief of cardiovascular medicine at the University of Southern California, says in the absence of details, it's hard to know if Jackson had a cardiac arrest or if he stopped breathing.

Cardiac arrest strikes without warning. It occurs when the heart's electrical system goes haywire and the heart suddenly stops beating. It can occur after a heart attack or be caused by other heart problems. Medical experts say fewer than five per cent of those who suffer cardiac arrest survive.

Worries over prescription drug intake

Some of the Jackson family's associates have hinted that Jackson may have been taking too many prescription medications. Family attorney Brian Oxman told CNN on Thursday he believes the singer was overmedicated with prescription drugs.

"I have warned that one day Michael Jackson would wake up dead and that I would not be silent if that was the case — because of the misuse of medications," Oxman said.

Detectives from the Los Angeles Police Department's robbery homicide division searched Jackson's home overnight, but said the investigation was standard procedure for high-profile cases.

With files from The Associated Press