DEA experts and the U.S. Attorney's Office have been drafted in to help Carver County Sheriffs determine the cause of the Purple Rain singer's death.

"The DEA and U.S. Attorney's Office are able to augment this local investigation with federal resources and expertise about prescription drug diversion," a spokesperson for the US Attorney's Office told Entertainment Tonight. "While this remains an ongoing investigation, we will have no further comment."

A law enforcement source previously told CBS News that prescription drugs were found in Prince's possession at the time of the singer's death.

The news of the DEA's involvement comes hours after Dr Howard Kornfeld, who runs Recovery Without Walls in Mills Valley, California, was contacted by Prince's aides on the night before his death because the singer was "dealing with a grave medical emergency."

Kornfeld specialises in opioid addiction treatment.

Prince was found unresponsive in an elevator at his Paisley Park home in Minnesota on 21 April (16), amid reports suggesting he was battling a prescription painkiller issue.

An autopsy carried out on Prince's remains on the day after his death proved inconclusive and now experts are awaiting the results from tests to determine how the music icon died.