Now a small-scale study stated that doctors might be supporting mercy killing by administering fatal morphine doses to children dying of cancer at their parents' request.

A few parents accepted that they had asked doctors to speed up death of their children who were in pain and doctors did so using high doses of the powerful painkiller.

However, study’s lead author and other physicians said they doubt doctors were active in mercy killing.

Lead author Dr Joanne Wolfe, a palliative pain specialist at Dana-Farber Cancer Institute and Children's Hospital in Boston, said that the deaths were coincidental by increased morphine doses by doctors to ease pain.

Doctors from American Academy of Pediatrics and American Medical Association oppose mercy killing but say it can be ethical to withhold life-prolonging treatment for dying patients.

Dr Douglas Diekema, a medical ethicist at Seattle Children's Hospital, said the study results are not surprising.

"I have no doubt that in a small number of cases, some physicians might cooperate with a parent's desire to see a child's suffering ended. This might include giving a drug for sedation or pain control that also suppresses the drive to breathe.”

Among parents studied, parents of five children said they had requested their doctor for euthanasia for their dying children, and parents of three said it was done with morphine.