SYDNEY - Australia's Treasurer Wayne Swan came under pressure to resign immediately on Saturday over allegations that he and Prime Minister Kevin Rudd abused their power and misled parliament.

But Swan denied wrongdoing and hit back at the claims, suggesting opposition politicians may have played a role in faking emails purporting to show the prime minister and treasurer misused used their positions.

Opposition leader Malcolm Turnbull called for Swan, in charge of steering Australia through its economic crisis, to quit immediately over his alleged role in trying to secure a government loan for a car dealer friend of Rudd.

"Mr. Swan has offered no explanation for any of this and today should tender his resignation," Turnbull said in a statement.

"He has misled the parliament and used the enormous influence of the commonwealth government to seek to secure an advantage for a mate and benefactor of the prime minister," he said.

The opposition had Friday called on Rudd and Swan to either explain their roles in helping car dealer John Grant seek a loan or resign.

Turnbull upped the ante on Saturday, claiming Grant was given "extremely favourable treatment by treasury officials and Mr Swan was kept closely and personally informed".

Rudd told parliament this month that neither he nor his office had lobbied the treasury on behalf of Grant, a former neighbour of the prime minister who has also provided a van for use by Rudd's campaign.

Swan told parliament his office had simply passed on representations on behalf of Grant but said he did not know the outcome of the correspondence.

Rudd late Friday announced an inquiry into the scandal after a senior treasury official told a parliamentary committee he thought he had received an email from Rudd's office asking him to look into funding for Grant.

Sydney's Daily Telegraph newspaper Saturday published an email allegedly confirming Rudd's office tried to secure a taxpayer-funded loan to Grant from the two-billion-dollar (1.6 billion US) OzCar vehicle financing scheme.

The emails indicate that correspondence about a loan for Grant was also faxed to Swan's home.

But Swan denied any impropriety and said it was up to the opposition to prove it was not involved in faking the emails.

"I think the opposition has a responsibility to come out today and to rule out any role in the creation, distribution or promotion of that fake email," Swan told reporters.