Australia has defended its agents' raid on the office of a lawyer for East Timor last month as a legitimate defence of Australian national security.
East Timor is asking the United Nations' highest court to order Australia to hand to the court documents and data seized in the raid in Canberra pending resolution of a case into the legality of the raid.
The case at the International Court of Justice is the latest step in a high-stakes legal battle between resource-rich and wealthy Australia against its tiny and impoverished northern neighbour over carving up the oil and gas reserves under the sea that divides them.
Australia's agent to the court, John Reid, told judges the raid was "a lawful and legitimate protection of ... national security."
The case in The Hague was triggered when Australian intelligence raided the office of lawyer Bernard Collaery and a former spy who intended to testify in an arbitration hearing that Australia allegedly bugged the East Timorese Cabinet ahead of sensitive oil-and-gas revenue-sharing negotiations.
Australia argued its raids were justified because the spy's plan to testify amounted to a possible national security breach.
East Timor "seeks to prevent Australia taking steps properly available to us under domestic law ... to protect ourselves from a threat to security apparently posed by a disaffected former officer," said lawyer Justin Gleeson.
Lawyers for Australia also said the court does not need to order Canberra to hand over the documents because Attorney-General George Brandis already has pledged not to allow the seized information to be used for any purpose other than possible action to safeguard national security.
East Timor has expressed fears that the information in the seized documents could be used in the arbitration case.
In that case, at another Hague-based legal institution, the Permanent Court of Arbitration, East Timor is challenging the validity of a bilateral treaty struck with Australia in 2006 over sharing seabed oil and gas reserves worth billions of dollars.
East Timor argues that the 2006 treaty is invalid because Australia had illegally bugged government offices and listened to confidential discussions relating to the negotiations.
"It is simply unconscionable that one party to negotiations or litigation should be able to place itself by these means in such a position of advantage over the other," lawyer for East Timor, Elihu Lauterpacht told the court Monday.