Bougainville's government has accused Papua New Guinea's leaders of breaching a landmark agreement between the two parties following PNG's latest move against the autonomous region's vote for independence.

The Port Moresby parliament last week adopted a sessional order to facilitate how far MPs will deliberate on whether to ratify the result of Bougainville's 2019 non-binding referendum whereby nearly 98 percent of the island's people had voted for independence from PNG.

Autonomous Bougainville Government President Ishmael Toroama claimed the decision of the parliament to draft a formal sessional order — the temporary instruction adopted by a legislative assembly on how it conducts parliamentary business — without the required consent of the Speaker of Bougainville's House of Representatives amounted to a "breach of the Melanesian Agreement".

The agreement, which was signed between PNG and Bougainville at the Burnham military camp in Christchurch, New Zealand last year, committed both governments to collaboration, constitutional integrity and to a mutual understanding in navigating the Bougainville peace process of which the referendum was a core component.

However Mr Toroama said the latest move by parliament "runs contrary to principles of respect, good faith and partnership in the Bougainville Peace Agreement".

"I am disappointed in certain parts of the Prime Minister's statements, the order of the debate, and the unilateral position on the negotiated majority threshold," he said in an authorised statement.

The PNG parliament voted to adopt the order, which included setting a three-quarters absolute majority threshold that requires 75 per cent of the country's MPs to vote towards approving Bougainville seceding from the state by ratifying the referendum result from seven years ago.

The move throws away the expected standard two-thirds threshold which is often required for most other constitutional amendments by the country's parliament.

PNG Prime Minister James Marape responded to questions over the threshold margins and related issues last week, saying PNG and Bougainville had agreed to the absolute majority threshold as part of the sessional order that the autonomous region disputes.

Mr Marape said PNG would continue to adhere to the commitments it has made on Bougainville independence towards finding an acceptable way forward on the delicate position.

He added further consultations between the two parties on how to proceed to parliament making a decision on the referendum result would take place in July, with the Prime Minister previously indicating a final vote of MPs over Bougainville seceding from PNG was scheduled to go ahead by the end of August.

Mr Toroama has since called for support from the United Nations, asking for further international monitoring on the alleged breach of the Melanesian Agreement in a distinct sign of deteriorating relations between the de facto state and its inherited rulers.

He has previously stressed Bougainville's push towards self-determination is deeply rooted in cultural identity, historical experience, and decades of sacrifice by its people.

Bougainville was incorporated into Papua New Guinean independence in 1975 after nearly 90 years of colonial rule that included the island — along with the archipelago territories of New Guinea and Papua — being administrated by Australia after World War II.

"I now call on the facilitator appointed to support development of the Melanesian framework to activate that commitment to international monitoring and to convene a meeting of international partners, representatives of the international community and the international witnesses to the signing of the Bougainville Peace Agreement," Mr Toroama said, "to address the breach by the national government of its commitments under the Melanesian Agreement and ensure that the process and principles agreed at Burnham are honoured."

As of Tuesday PNG's government was yet to respond to the call for UN involvement.

Mr Toroama also repeated a warning to his fellow Bougainvilleans, saying their "resolve would be tested by events in the national parliament", urging the autonomous region's residents to just "remain calm, united, and respectful" during the taxing independence process.