Papua New Guinea Prime Minister Peter O'Neill has refused to go to police for questioning over allegations of public corruption.

Peter O'Neill was served with an arrest warrant in relation to a fraud case by the country's anti-corruption body.

The director of police crimes, Thomas Eluh, says they have given the prime minister time to hand himself, but they fully intend to arrest him if he doesn't show up for questioning.

Mr O'Neill has told SBS News the warrant against him is politically motivated.

"There is a lot of political movement in the country," he said.

"(The opposition) are using any avenue possible to try and discredit government and of course find a way to have me arrested.

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"We have strong confidence in the judiciary up here, there is a very vibrant judiciary that will hear the matter and the truth will come out."

It is unclear who signed the arrest warrant, as Police Commissioner Tom Kulunga is out on bail while appealing a sentence of seven months with hard labour on three contempt charges.

The legal action relates to millions of dollars of alleged illegal payments from the government to a law firm, led by Paul Paraka.

A letter signed by Mr O'Neill seeming to authorise some of the payments was produced previously.

Mr O'Neill has claimed it to be a forgery.

"We have no record of that matter whatsoever in my office and every letter that goes out from this office is registered and then delivered," he said.

"The letter...is addressed to one party and delivered to another and on that basis we understand that the letter did not originate from our office.

"I can strongly deny any involvement in that letter."

Fairfax Media is reporting Australian forensics experts have analysed the document in question.

PNG investigators say they also have a subsequent letter by Mr O'Neill in which he attempts to clarify his previous letter, and in doing so, confirms the existence of the letter in question.

In January, the anti-corruption unit said it had no case against Mr O'Neill and that no further investigations would take place unless fresh evidence emerged.

Papua New Guinea's multi-agency anti-corruption unit, the Investigation Task Force Sweep, charged one of the nation's largest law firms in October with offences including conspiracy to defraud, stealing by false pretence and money laundering.

Task Force Sweep has alleged Paraka Lawyers submitted fraudulent bills for legal work performed for the state then received payments from PNG's finance department.