Federal Attorney-General Nicola Roxon has blocked the release of cables about East Timor, despite the fact they are up to 37 years old.

Ms Roxon decided to keep the documents secret on the grounds that opening them up would prejudice Australia's security.

Associate Professor Clinton Fernandes of the University of New South Wales believes the documents are being kept secret because they would reveal Australian complicity in concealing the mass starvation of 100,000 East Timorese.

Professor Fernandes, a former Army intelligence officer who had one of the highest security clearances, requested the documents from the Federal Government.

He told PM the Foreign Affairs Department even demanded secrecy for its reasons for hushing up the documents.

"The Attorney-General has gone to water (with) the first whiff of grapeshot," he said.

"She should have exhibited a bit more scepticism about claims on intelligence and national security. She hasn't done that.

"The Attorney-General has signed a certificate withholding even the reasons why they want the material kept secret.

"I wrote to her warning her against the possibility of being dazzled by claims as to sensitivity risk and security. I guess she just accepted whatever advice she was given."

Professor Fernandes says he knows what the documents are about.

"The documents relate to cables written by the Australian Embassy in Jakarta back to Department of Foreign Affairs headquarters in Canberra in the late 1970s, and the documents also relate to profiles of Indonesian leaders in the early 1970s," he said.

"The big problem with keeping them classified is that Indonesia has democratised; everything has changed.

"Suharto is not only out of office, he's actually dead. Nobody from that era is likely to be offended to the point where we couldn't do international relations and diplomacy with them."

He speculates the documents are being protected to hide Australian knowledge of the reasons for a massive famine in East Timor after Indonesia invaded.

"There was massive famine, about 100,000 people dying in the space of a year out of a population of 640,000, so one of the largest losses of life relative to total population since the Holocaust," he said.

"This famine occurred as a result - the direct result - of Indonesian military operations.

"Australia, I believe, had knowledge of this and chose to cover it up in order to protect the relationship with the Indonesian dictatorship.

"This would cause embarrassment to Australian diplomats, but it certainly wouldn't harm Australia's national security. I believe embarrassment is really what's being protected here."

History of secrecy

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Professor Fernandes says the Department of Foreign Affairs does not have a culture of openness and transparency.

"Unlike in other countries, where materials are automatically brought onto the public record, here we have to ask for them, and if they say no we've got to go to court," he said.

"So it's prohibitively expensive and time consuming, except for those like me who happen to be at a university and can run cases."

And he says there is a long history of the Department of Foreign Affairs concealing documents about Timor and Australia's role there.

"The leaks of intelligence and cables that occurred in the 1970s exposed the fact that national security was being used as an alibi, not as a goal," he said.

"From the '70s, '80s, '90s there's been a long history of deception, and unfortunately what's happened now is that the Attorney-General has allowed the department to once again shield itself.

"Really what ought to happen now is that the Foreign Minister Bob Carr should intervene personally and simply declassify the documents."

Professor Fernandes says Ms Roxon's action are in contrast to statements she made while in opposition.

"In opposition she was talking about the importance of being open, transparent and the need to prevent the government holding on to materials that don't unnecessarily compromise national security," he said.

"The fact is that we don't know what these documents are or whether they will compromise national security because the same Nicola Roxon has signed a certificate preventing us even knowing the reasons."