Jakarta - Indonesian prosecutors will appeal the acquittal of a former intelligence agency official accused of masterminding the murder of a leading human rights activist, a spokesman for the Attorney-General's Office said Friday.

Activists have criticized the acquittal of Muchdi Purwoprandjono in the murder of Munir Said Thalib as proof that powerful figures remain above the law, despite a pledge by President Susilo Bambang Yudhoyono to get to the bottom of the case.

Judges at the South Jakarta district court on Wednesday found Muchdi not guilty of the charges, arguing that the prosecutors had failed to provide evidence to back up their indictment. Muchdi has denied any wrongdoing.

Munir died of arsenic poisoning on board a Garuda Indonesia flight from Jakarta to Amsterdam via Singapore in September 2004.

"We will lodge an appeal to the Supreme Court as soon as possible," said Jasman Panjaitan, a spokesman for the Attorney-General's office.

Panjaitan said prosecutors were still studying the verdict.

Government prosecutors had sought a 15-year jail sentence for Muchdi, 59, a former Military Special Forces general and deputy head of the State Intelligence Agency.

New York-based Human Rights Watch said in a statement a day before the verdict was passed that there were concerns that witnesses may have been coerced by powerful forces within security agencies.

During the court proceedings, all prosecution witnesses - many of whom were intelligence officials - either failed to show up, or retracted statements they had provided to police during initial investigations.

The only significant evidence the prosecutors had was purely circumstantial - records of 40 phone calls between former Garuda Indonesia pilot Pollycarpus Budihari Priyanto and Muchdi in the period leading up to Munir's murder.

Pollycarpus is now serving a 20-year jail sentence after the Indonesian Supreme Court last year found he laced Munir's orange juice with arsenic. Former Garuda chief Indra Setiawan was also jailed for one year for his role in the murder. (dpa)