Image caption Mr Brandis said the seizures were not intended to affect the case in the Hague

Australia has defended a raid on the offices of a lawyer representing East Timor in a case against Australia at an international court at The Hague.

Attorney General George Brandis said search warrants were executed, with documents and electronic media taken.

Lawyer Bernard Collaery is leading East Timor's case, launching on Thursday at the Permanent Court of Arbitration.

East Timor alleges Australia bugged key officials ahead of talks on a major energy deal.

The case centres on claims that the Australian Secret Intelligence Service (ASIS) used listening devices, planted in East Timor's cabinet office under the guise of refurbishment, to obtain information about a Timor Sea gas treaty in 2004.

The Certain Maritime Arrangements in the Timor Sea (CMATS) treaty sets out how Australia and East Timor share reserves.

East Timor now wants the treaty scrapped on the grounds that the alleged spying gave Australia an unfair advantage in commercial negotiations.

Speaking from the Hague, Mr Collaery said correspondence related to the case was taken. He described the raid as an intimidatory tactic.

A key witness in the case, a former senior Australia intelligence officer, was also questioned and had his passport cancelled to prevent him testifying, Mr Collaery and Australian media reports said.

Mr Brandis has not confirmed the passport cancellation. But he said that reports that warrants were issued "to affect or impede the current arbitration" were "wrong".

Material seized in the raids was "not under any circumstances to be communicated to those conducting those proceedings on behalf of Australia", he said in a statement.

Prime Minister Tony Abbott said the move was about protecting Australian interests.

"We don't interfere in cases but we always act to ensure that our national security is being properly upheld - that's what we're doing," he said.