An Indonesian court has found a young US couple guilty of murdering the woman's mother and stuffing her battered body into a suitcase on the resort island of Bali.

Heather Mack and Tommy Schaefer, both from the Chicago area, were arrested last August after staff at a luxury hotel discovered the body of Mack's mother Sheila von Wiese-Mack in an abandoned suitcase in a taxi.

Schaefer was sentenced to 18 years in prison for premeditated murder immediately after the verdict was delivered by a panel of three judges and Mack to 10 years for being an accessory to murder.

The pair were tried separately in Denpasar District Court and it was not immediately clear if they would appeal.

Schaefer, 21, who had said in court he had killed Wiese-Mack in self-defence after she attacked him in anger because she objected to the couple's relationship, apologised to the family of the victim.

"Although I do take full responsibility for my actions, I am not a murderer," he said.

Prosecutors had called for a 15-year sentence for Mack, 19, because she faced a lesser charge and because she recently gave birth to a baby girl.