A former head of Indonesian carrier Garuda and another airline official have been arrested in connection with the murder of a leading rights campaigner who was poisoned during a flight, an airline lawyer said.

Munir Thalib, known for his critical views on the military, was murdered during a flight on Garuda when he was on his way to the Netherlands for postgraduate studies in 2004.

In October, the Supreme Court overturned the guilty verdict of off-duty pilot Pollycarpus Budihari Priyanto in the murder case, saying there was not enough evidence and no witness to support the case.

The acquittal put pressure on President Susilo Bambang Yudhoyono, who had vowed to get to the bottom of the case when he took office in late 2004.

"Our clients, Indra Setiawan, former president director of Garuda, and Rohainil Aini, a flight operations officer, were arrested and are being held by the police at this moment," Garuda's lawyer, M. Assegaf, told reporters.

"Indra Setiawan and Rohainil Aini are suspected of aiding Pollycarpus in the murder of a person, in this case, Munir," he said.

"We will study this arrest carefully because Pollycarpus, who was investigated and brought to court by the help of Indra Setiawan and Rohainil, was acquitted by the court."

On Thursday, the Indonesian police chief said two new suspects had been named in the probe because of their links to issuing a fake document that allowed Priyanto to be on board under the pretense of a security assignment. He did not reveal the names of the two suspects.

A district level court had sentenced Priyanto to 14 years' jail in December 2005 and an appellate court upheld the finding he put arsenic in food served to Munir.

However, the Supreme Court ruled there was not enough evidence and no witness to support the case.

Munir was an outspoken critic of the military and its methods in quashing dissent and separatists in hotspots such as Aceh and Papua provinces.

A Garuda Indonesia pilot himself, Priyanto had said he was on an assignment supervising security on the Jakarta-Singapore leg of Munir's flight. He gave his business-class seat to Munir during that leg.

Human rights groups say the government has not pressed the investigation or Priyanto's possible ties to others hard enough.