Jakarta – Indonesia's Supreme Court has upheld the acquittal of a former senior spy accused of ordering the deadly poisoning of human rights activist Munir Said Thalib, a spokesman said Friday.

The court rejected an appeal by prosecutors against the December acquittal by a Jakarta court of former State Intelligence Agency deputy director Muchdi Purwopranjono over the 2004 killing, Hatta Ali said.

Purwopranjono was accused of ordering the killing of the outspoken military critic, who died of arsenic poisoning on a Garuda Indonesia flight from Jakarta to Amsterdam via Singapore.

"The supreme court judges issued the ruling on June 15 that an appeal filed by prosecutors against the acquittal of (Purwopranjono) cannot be accepted," Ali said. "The prosecutors failed to provide (the necessary) evidence to overrule the acquittal," he said.

Former Garuda boss Indra Setiawan and pilot Pollycarpus Priyanto were previously handed jail terms over the poisoning, but activists have long accused senior spies of being behind it.

Pollycarpus was jailed for 20 years last year for carrying out the poisoning, while Setiawan was sentenced to a year in jail for being an accomplice.

The case has been seen as a test of how far Indonesia has come in curtailing the power of the military since the 1998 fall of the country's former dictator Suharto.