WikiLeaks founder Julian Assange may have broken Australian law and may not be welcomed back to the country if convicted, Attorney-General Robert McClelland says.

Mr Assange, who has been involved with the online posting of about 250,000 US diplomatic memos, is the subject of a Swedish arrest warrant over sex-crime allegations.

He was born in and holds a passport for Australia and may return to the country.

"I'm aware the US Attorney has said that US law-enforcement authorities are looking very closely at the fact that United States laws may have been breached and the Australian Federal Police are looking at whether any Australian laws have been breached," Mr McClelland told reporters on Saturday.

"We have also indicated that we will provide every assistance to United States law-enforcement authorities."