The most successful anti-corruption agency in Papua New Guinea's history has been starved of funding and is broke, as a result of allegations made against prime minister Peter O'Neill.

Taskforce Sweep has 350 cases currently under investigation and 91 cases before the courts, after securing high-profile convictions and international praise.

However, PNG has cut funding to the multi-agency investigator and to other key parts of the nation's anti-corruption efforts.

"At the moment we've run out of funding and I'm running a skeleton staff," Taskforce Sweep chairman Sam Koim.

Most of the agency's investigators have returned to their jobs within the police force and Mr Koim has not been paid for months, despite a court order allowing Taskforce Sweep to continue its work.

The moves come despite repeated promises to tackle corruption in PNG, which ranked 145 out of 175 countries in a global transparency index last year.

"Overall we had the impression Taskforce Sweep was doing a particularly good job and starting to crack through some of the hard issues," Transparency International PNG chairman Lawrence Stephens said.

The taskforce's investigations led to the jailing of MPs Paul Tiensten and Francis Potape for corruption.

Prominent lawyer Paul Paraka was also charged and currently faces court for disputed legal bills allegedly approved by Mr O'Neill.

Promised money never paid to taskforce

On paper, the National Anti-Corruption Strategy Taskforce had its budget cut from $9.2 million to $2.3 million for 2015. But the reality is far bleaker.

Money allocated to Taskforce Sweep last year never arrived and the agency has been surviving on the $2.6 million it received in 2013.

"We based our operations on the funding that was released to us in 2013 and in 2014 we didn't receive any toea [cent] from the government, despite numerous requests for those funds," Mr Koim said.

It is not clear what happened to the $9.3 million (20 million kina) allocated to the prime minister's office in 2014 to run Taskforce Sweep.

The prime minister's office directed the ABC's inquiries to treasury but repeated attempts to get information from PNG's treasury have been unsuccessful.

The Australian taxpayer funds several well-paid experts to advise the PNG treasury, as part of the Strongim Gavman (Strengthening Government) aid program, but none were allowed to comment.

"Out of that [20 million kina budget for the National Anti-Corruption Strategy Taskforce], seven million kina was earmarked for Taskforce Sweep operations," Mr Koim said.

"None of that was released to us despite many follow-ups and requests for the drawdown of those funds."

Former attorney-general Kerenga Kua wrote to the prime minister on January 16, 2013, trying to find out where anti-corruption money went, but received no reply.

"I understand that Task Force [Sweep] was established to oversee the implementation of the National Anti-Corruption Strategy, spearheaded by your department," said Mr Kua, who was sacked in the fallout from the corruption allegations against Mr O'Neill.

"I therefore seek your clarification on whether Taskforce Sweep is included under that K20 million funding and if so, how much of this money is appropriated for Task Force Sweep operations," he wrote.

"There is no reference to Task Force Sweep anywhere in the budget books."

Taskforce Sweep was set up in 2011 by Mr O'Neill, but after being served an arrest warrant for official corruption in June 2014, the prime minister disbanded it.

A court overturned the decision, ordering that Taskforce Sweep be allowed to continue its work.

PNG on 'grey list' for money laundering, terrorist financing

Taskforce Sweep is not the only important PNG agency to be hit by a funding crisis.

The police Financial Intelligence Unit, which deals with money laundering, was allocated $312,000 for 2015, less than the police band's budget of $419,000.

This is despite the imminent threat of an international blacklisting for potential money laundering.

"If you see that the police band is getting more money than other very important things, you have to start questioning ... the priorities for fighting corruption, for fighting fraud," Mr Stephens said.

In early 2014, the international Financial Action Task Force placed PNG on a 'grey list' of countries open to money laundering and terrorist financing.

The Financial Intelligence Unit is supposed to be working on an action plan to improve PNG's performance and keep it off the blacklist, but the head of the police National Fraud & Anti-Corruption directorate told the ABC that is not happening.

Chief Superintendent Mathew Damaru said funding promises by the government's chief secretary in February 2014 were not followed through after the PM's arrest warrant was served by Mr Damaru's officers in June.

Failure to address weaknesses in PNG's money laundering systems will lead to the nation being considered a "high risk and non-cooperative" country in terms of money laundering and terrorist financing.

Chief Superintendent Damaru said PNG is "heading for the blacklist".

This will place PNG in the company of North Korea and Iran, and would discourage international investment.

Corrupt officials 'wash' money in Queensland real estate

Despite the 75 per cent cut in funding for PNG's main anti-corruption effort, other related areas did receive a boost in PNG's 2015 budget.

The police National Fraud & Anti-Corruption unit received a 39 per cent increase to $718,000, despite being branded "rogue" officers by the PM's legal team after serving the arrest warrant on Mr O'Neill.

The auditor-general, ombudsman, Internal Revenue Commission and the judiciary were all promised more money for 2015.

Improving governance and helping fight corruption is a key goal of Australia's $517 million aid program in PNG this year.

The Combating Corruption Project, delivered by AUSTRAC and the Attorney-General's Department, is spending $2.5 million "to enhance ... the PNG financial system against money laundering, corrupt activity and terrorist financing".

Other programs support the work of the ombudsman, police and the courts.

Investigators say Australian bank accounts and Queensland real estate are the top ways corrupt PNG officials "wash" their stolen money.

After almost 40 years of independence from Australia, Papua New Guinea has gone backwards in many key social and health areas, and is one of only a handful of countries set to meet none of the UN Millennium Development Goals.