Australian swimming officials have demanded an explanation about the leaking of an alleged doping investigation involving retired Olympic champion Ian Thorpe.

Swimming Australia chief executive Glenn Tasker said neither Thorpe nor the national body had been told about any irregularities until the claims were published in the French newspaper L'Equipe.

• The Amphibian

"Somebody has leaked the information and (Thorpe's) privacy has been grossly invaded," Tasker told a news conference on Saturday.

"We don't know where the leak is... (but) we believe FINA (swimming's world governing body) have to do something about it. Whether that leak has come from any (doping) agency I think is very, very poor."

Tasker said Thorpe, who retired last year as one of the most decorated swimmers in history, had the full backing of Swimming Australia.

•  Thorpe of our time

"I will support Ian 1,000 percent," Tasker said.

"He is a young man with unbelievably strong principles and integrity."

Australia Prime Minister John Howard also offered his public support to Thorpe.

"I don't intend to react to, let alone endorse, unsubstantiated allegations in a French newspaper," Howard told reporters.

"As far as I'm concerned, until solid evidence of the contrary is produced, Ian Thorpe remains a great Australian champion."

FINA confirmed on Saturday that it had lodged an appeal with the Court of Arbitration for Sport (CAS) over a doping test conducted by the Australian Sports Anti-Doping Authority but did not name the swimmer involved.

FINA said there was no evidence of a positive test but there had been an "adverse analytical result" that it had referred to CAS "with the aim of clarifying the issues surrounding the case".

The news sent shockwaves around the World championships in Melbourne with swimmers and coaches speaking out in support of Thorpe.

"I find it astonishing that it's done at this time," Canadian head coach Pierre Lafontaine told reporters.

"I can only tell you that (Thorpe) has been a great ambassador for sports all around the world and I would be very surprised (if it were true)."