German prosecutors said on Wednesday they charged a Berlin palliative care doctor with the murder of 15 patients, alleging he acted out of a "lust" for killing.

The 40-year-old suspect is accused of having killed 12 women and three men between September 2021 and July 2024 using a deadly cocktail of sedatives.

German press reports identify the suspect as Johannes M, but prosecutors have not released a name.

The doctor allegedly "administered an anaesthetic and a muscle relaxant to his patients... without their knowledge or consent", the Berlin prosecutor's office said.

The relaxant "paralysed the respiratory muscles, leading to respiratory arrest and death within minutes".

The victims, who were all receiving care at the time, were aged between 25 and 94 years old.

On five occasions, prosecutors alleged that the suspect had "set fire to their apartments to cover up these killings".

The list of accusations against the suspect has grown in length and severity since his initial arrest in August.

The suspect was originally held on suspicion of manslaughter in relation to four deaths.

Prosecutors subsequently said in November they were treating the alleged killings as murder cases, adding four more deaths to the list of accusations.

"The accused appears to have had no motive for killing the people other than the act of killing itself," prosecutors said at the time.

The suspect had nothing other than a "lust for murder", they said.

Prosecutors said they were seeking a "lifelong professional ban" and called for the suspect to be locked in "preventative detention".

A special team of investigators had identified a total of 395 suspicious cases that needed to re-examined in light of the accusations against the doctor. (AFP)