JAKARTA - A district court in Jakarta has found Indonesian Jessica Kumala Wongso guilty of pre-meditated murder and sentenced her to 20 years in jail for poisoning her friend Mirna Salihin by lacing her coffee with cyanide at a cafe in January.

The court said the prosecution had proven "convincingly" that Jessica, who is also an Australian permanent resident, had committed the crime.

"Her actions had caused the death of Wayan Mirna Salihin," said presiding judge Kisworo. "Her action towards her own friend is deplorable and sadistic... she was not remorseful and did not confess to her actions."

The 28-year-old had sat calmly before the judges, occasionally fidgeting, as the court's findings were read out.

In response to the verdict, Jessica called the 20 years' jail sentence "unfair and excessive". Her defence team also said they intend to file an appeal against the court's decision.

The verdict televised live by several Indonesian news networks has been followed closely since the trial began in June.

The case has also generated interest in Australia where Jessica and the victim had studied together at a design college.

Jessica has always maintained her innocence but prosecutors have been demanding that she be jailed 20 years for the murder of Ms Mirna, 27, who collapsed and died after drinking the poisoned coffee at an upmarket Jakarta cafe.

Jessica had denied she had premeditated the murder when she took the stand on Oct 12, telling the court: "I swear, I am not a murderer... I didn't kill Mirna so there shouldn't be any reason to treat me like garbage."

Prosecutors had argued that Jessica killed Ms Mirna after the victim urged her to end her relationship with her boyfriend over his alleged drug use.

They also said that Jessica, who was living in Sydney until last year, had planned the murder "meticulously" before inviting Ms Mirna to the cafe where she slipped cyanide into her iced coffee.