Police in Los Angeles have said they have opened an investigation into the death of actor Matthew Perry.

Perry, the star of the hit TV sitcom Friends, died in October from "acute effects of ketamine", medical officials said at the time.

The investigation will look into how the actor obtained the anaesthetic ketamine found in his system.

Drowning was also listed as a contributing factor in his death, which was ruled an accident.

In a statement to media on Tuesday, the Los Angeles Police Department confirmed that it is working with the Drug Enforcement Agency and the US Postal Inspection Service on an investigation into the 54-year-old’s death.

It is unclear how far along the investigation - which was first reported on by TMZ - is or who has been interviewed as part of it.

Perry was found unresponsive in the pool of his LA home on 28 October and was later pronounced dead at the scene.

The LA County medical examiner’s office said in December there were “high levels of ketamine found in his post-mortem blood specimen”.

Senior deputy medical examiner Raffi Djabourian added that other contributing factors in his death were coronary artery disease and the effects of buprenorphine, which is used to treat opioid use disorder.

"Drowning contributes due to the likelihood of submersion into the pool as he lapsed into unconsciousness; coronary artery disease contributes due to exacerbation of ketamine induced myocardial effects on the heart,” he said.

Perry had been receiving medically supervised ketamine treatments for depression and anxiety at the time of his death, though the report noted that his last prescribed ketamine treatment was a week and a half before his death.

At the height of his fame, Perry was battling with addiction to painkillers and alcohol, and attended rehabilitation clinics on multiple occasions.

In 2016, he told BBC Radio 2 that he could not remember three years of filming during Friends, because of drink and drugs.

After attempts at treatment, he wrote in his memoir that he had been mostly sober since 2001 - "save for about 60 or 70 mishaps".