Canberra – Nobel peace laureate Jose Ramos Horta Tuesday accused the Australian government of covering up Indonesia's involvement in the deaths of five Australian journalists in East Timor 22 years ago.

Australia's 1996 investigation into the killings was seriously flawed, the leading East Timorese independence activist said, joining calls into a fresh inquiry.

"Those journalists were murdered. It was premeditated, preplanned murder," he told ethnic broadcaster SBS radio here from Austria, where he was attending a conference on East Timor.

Jakarta has always denied allegations the men were murdered by Indonesian troops and Australia's Sherman commission found it was likely they lost their lives in crossfire in the heat of battle.

"I was very disappointed with the Sherman report," Ramos Horta said.

"There was no crossfire there on October 16, 1975. The area had been vacated by the Fretilin (independence) troops. The journalists were caught by the Indonesians and then executed in cold blood."

Australian officials in Indonesia at the time had heard radio transmissions where Indonesian military officials boasted about the killings and threatened more, he said.

Ramos Horta questioned whether Australia was interested in finding out the truth about Balibo, saying it was motivated by a fear of upsetting its northern neighbour.

"The Australia, New Zealand and British governments all decided to sacrifice their citizens... for the sake of their commercial and diplomatic relations with Indonesia," he said.

The 78-year-old mother of one of the journalists, Malcolm Rennie, has returned to Australia from her home in Britain to try to uncover the truth about her son's death and recover his remains.

Wilhelmina Rennie said the British and Australian governments failed to fully inform her of the details surrounding her son's death.

"I would really like an apology from our own government and the Australian government for keeping us in the dark for 21 years," she told reporters here.