Melbourne, Sep 1 (IANS): A woman in Melbourne was Wednesday jailed for 27 years for killing her two minor sons in what she termed as her "greatest act of love".

Qualified nurse Donna Fitchett, 51, drugged, strangled and smothered her two sons -- Thomas, 11, and Matthew, nine -- at their home on Sep 6, 2005.

She admitted she murdered her children but pleaded not guilty by reason of mental instability. She said her depression led to their deaths because she intended to take her own life and felt she could not leave the boys behind.

But Supreme Court Judge Elizabeth Curtain Wednesday termed Fitchett's actions as her "greatest act of betrayal", the Sydney Morning Herald reported.

"You were their mother. Your responsibility was to nurture, care for, love and protect them and over the years you did that," Curtain said.

"But in the greatest act of betrayal and in a profound breach of trust, you robbed each of them of their precious lives... in an act of unfathomable selfishness."

Curtain said the murder was premeditated, citing a letter Fitchett had written to her psychologist before she killed the boys.

"You knew what you were doing, you contemplated it, planned it and wrote about it, before you did it," the judge said.

Curtain said Fitchett had "altered for all time the lives of David Fitchett and created unbearable, unforgiving pain for him and his family".

"No sentence this court gives can restore life to their sons, or peace to their father," she said.