A postmortem into the death of George Michael has come up inconclusive, police have reported. 

According to ABC, authorities have said more tests will need to be run to determine the cause of the iconic singer's death. 

"A post mortem examination was carried out yesterday as part of the investigation into the death of George Michael," Thames Valley police said in a statement.

"The cause of death is inconclusive and further tests will now be carried out. The results of these tests are unlikely to be known for several weeks."

Michael passed away in his southern-England home on Christmas Day.

His manager, Michael Lippman, reportedly said he died of heart failure.