Russian investigators say two sisters who killed their father after years of abuse should face murder charges in a closely watched case that has fueled a debate on domestic violence in the country.

The teenage Khachaturyan sisters -- Maria, Angelina, and Krestina -- stabbed their father to death in a Moscow suburb in July 2017 after enduring what they say was constant humiliation and sexual abuse.

The Investigative Committee said on December 3 that it had completed the investigation into the killing and was recommending charges of murder and conspiracy to commit murder against the two older sisters, Krestina and Angelina, who were aged 18 and 19 at the time.

The statement said the two were of sound mind and aware of their actions when the killing occurred, but it also pointed to the long-term "physical and mental suffering" inflicted on them by their father as a mitigating circumstance.

They face up to 20 years in prison if convicted of the charges.

Investigators recommended that the third sister, Maria, who was 17 at the time of her father's killing, should enter mandatory psychiatric care.

The investigation established that the sisters, acting as a group, stabbed their father with a knife and beat him with a hammer on his head, neck, chest, and other parts of his body, causing fatal wounds.

Mari Davtyan, a lawyer for Angelina, told AFP that the sisters "used reasonable force in self-defense."

The three sisters have confessed to using a knife and a hammer to kill their 57-year-old father, Mikhail Khachaturyan.

They been kept under limited house arrest and subjected to various restrictions since their father was found dead in his apartment.

The case has received broad coverage in the media in Russia and abroad, and has triggered a debate on domestic abuse following the 2017 introduction of a law decriminalizing most forms of battery.

With reporting by AFP