Attacking Prime Minister Julia Gillard for being "clumsy", the opposition has criticised her for failing to pinpoint any Australian law broken by the whistleblower website WikiLeaks.

Stating that the 'foundation stone of it was an illegal act', Gillard failed to answer on which Australian laws were broken by either WikiLeaks or Assange.

She said the Australian Federal Police were investigating.

"The foundation stone of it is an illegal act," Gillard said today, adding, "It would not happen, information would not be on WikiLeaks, if there had not been an illegal act undertaken", AAP reported.

"It's grossly irresponsible and anybody who looks at the pages of today's newspaper and sees that things like critical infrastructure lists are being put on WikiLeaks ... would understand how grossly irresponsible this is," Gillard said.

A classified cable listing infrastructure critical to the US was published by the site overnight.

The list included some Australian-based infrastructure including the already widely known undersea telecommunications cable - the Southern Cross Cable.

Opposition Legal Affairs spokesman George Brandis accused Gillard of being "clumsy" with her language on the issue of illegality.

"As far as I can see, he (Assange) hasn't broken any Australian law," he said adding "Nor does it appear he has broken any American laws."

Senator Brandis, a Queen's Counsel, called for any debate about the publishing of the cables to have a well-defined understanding of the difference between something which appeared to be morally wrong and an act which was illegal.