CANBERRA - Australian police will investigate whether someone impersonated a public servant and concocted a 'fake' email suggesting that Prime Minister Kevin Rudd abused his powers, Rudd said Saturday.

Rudd's announcement came as the national opposition called for the prime minister and Treasurer Wayne Swan to resign for allegedly helping a car dealer neighbour of Rudd's secure a government loan and for misleading parliament over it.

Newspapers on Saturday published an email purporting to show that Rudd's office lobbied to secure a taxpayer-funded loan for car dealer John Grant from the A$2 billion (S$2.32 billion) OzCar vehicle financing scheme. But Rudd on Saturday dismissed the email as a political smear campaign and said police would investigate its source after opposition leader Malcolm Turnbull on Saturday said he did not have a copy of the email.

'There is no record of any such communications. Our only conclusion is that this alleged email is false and a fake,' he told reporters, adding that it was easy to 'throw mud' at political figures.

'It is time for some honesty from Mr Turnbull on this matter,' he said, accusing the opposition leader of doing an about-face on whether he had a copy of the 'false email' and calling on him to detail what he knows about it.

The prime minister said he had asked the attorney-general to refer the case to the Australian Federal Police because impersonating a public official was 'an extremely serious offence'.

Rudd urged Turnbull to commit to 'full cooperation' with the police inquiry.

Swan earlier Saturday also dismissed the email and suggestions that car dealer Grant was given preferential treatment when seeking a loan as part of a political 'smear campaign' fuelled by the opposition. Turnbull denied his party had played any role in writing or circulating the alleged email.