The former president of East Timor wants to give evidence on behalf of two Australians charged with sharing secret information.
Xanana Gusmao has warned his evidence is likely to embarrass the Australian government, renewing calls for Canberra to drop the prosecutions instead.
Former spy Witness K and lawyer Bernard Collaery are facing jail for allegedly sharing secret information with the government of East Timor in relation to the 2004 bugging of the prime minister's office in Dili by Australian foreign agents.
"I already promised to them, if it was not a secret trial, I will go to be their witness," Mr Gusmao told the ABC.
When asked what he would reveal in court, Mr Gusmao said: "All the information that I know."
Witness K has indicated he intends to plead guilty for allegedly conspiring to share secret information with East Timor over the spying operation.
He is due to appear before the ACT Magistrates Court on Thursday.
Collaery intends to fight the charges against him. He is due back in court in December.
The cases are expected to have a high degree of secrecy under the National Security Information Act passed in 2004 primarily to deal with terrorism cases.
Former Supreme Court judge Stephen Charles QC told the ABC's Four Corners it was hard to imagine any justification for the cases to take place in camera.
"Everyone who reads the newspapers is aware that ASIS officers entered and bugged the Timorese cabinet premises," he said.
"Everyone is aware that the result of bugging those premises was that Australia got a huge and very unfair advantage in the (oil and gas) negotiations being carried out between Timor and Australia."
Attorney-General Christian Porter told the ABC he had confidence the courts would strike the right balance between the need to protect national security and the principle of open and transparent proceedings.
"I have previously expressed the view that as far as it is possible, any legal proceedings in this matter should be conducted in open court, and this remains my view."
Mr Porter stood by the decision to prosecute, which had been based on on the commonwealth prosecutor's independent assessment of the evidence and external expert legal opinion.
Australian Associated Press