Australia, Papua New Guinea and Indonesia have started annual defence ministers meetings to build trust and boost military cooperation after a new defence treaty between Canberra and Port Moresby stirred anxieties in Jakarta.
Papua New Guinea has also raised concerns over its border with Indonesia, calling for the establishment of a new 10-kilometre "buffer zone" between the two countries, which military and government forces would be banned from entering.
It comes after Australia and Papua New Guinea inked a landmark mutual defence treaty in October, committing to defending each other in an armed attack.
Just over a month later, Australia and Indonesia announced they had concluded negotiations on their own security treaty, which is set to be signed in Jakarta by Prime Minister Anthony Albanese and President Prabowo Subianto in January.
But Papua New Guinean Defence Minister Billy Joseph told the ABC that Indonesia had "raised concerns" about the Australia-PNG pact.
Under the deal, known as the Pukpuk Treaty, Australia has promised to help bolster Papua New Guinea's defence force by supplying weapons, military equipment, holding joint exercises and training.
The treaty will also allow Australia to recruit Papua New Guinean citizens into its defence force and vice versa.
It is Australia's third military alliance and the first in more than 70 years since Australia forged the ANZUS pact with the United States and New Zealand in 1951.
Dr Joseph said Indonesia, which shares an 820-kilometre land border with Papua New Guinea, was worried about the potential implications of the treaty.
"They have raised a few concerns, especially with regards to their sovereignty," he said.
Dr Joseph said the idea for an annual trilateral defence meeting between the three nations came about when PNG was consulting with Indonesia over the new agreement.
"It's something that we all thought was a good idea because we are good neighbours," he said.
"Transparency has been the name of the game for us and we have nothing to hide."
First Australia-PNG-Indonesia defence meeting taking place tomorrow
Indonesia's foreign ministry spokesperson sounded a note of concern when the treaty was inked, saying while "Indonesia respects the right of every country to reinforce its defence system", no treaty should escalate "geopolitical competition" in the region.
"Indonesia also expects Australia and PNG to consistently uphold transparency in the process of forming this co-operation agreement, as well as to honour their commitment to respect the sovereignty and territorial integrity of neighbouring countries, including Indonesia," they said.
But Jakarta has since struck a much less wary tone, with top commander Agus Subiyanto declaring later in October that "Indonesia and Australia stand side-by-side in maintaining stability, security and peace across the Indo-Pacific region".
One Indonesian government source told the ABC that while there were still reservoirs of distrust in the Indonesian system when it came to the treaty, Australia had done a "good job" explaining what the Pukpuk Treaty was about and allaying those concerns.
The first meeting of defence ministers — featuring Dr Joseph, Australia's Defence Minister Richard Marles and Indonesia's Defence Minister Sjafrie Sjamsoeddin — will be held tomorrow morning in PNG's capital, Port Moresby.
One federal government source said the meeting could represent a "huge step" for Australia as it tries to build strategic trust between all three countries, although they cautioned that building trilateral military cooperation would take time.
The Indonesian government has been contacted for comment.
Papua New Guinea and Indonesia share an 820km land border
PNG proposes 'close collaboration' with Indonesia at border
Dr Joseph said PNG also held concerns about its border with Indonesia and the potential for tensions within West Papua to spill over into Papua New Guinean territory.
Indigenous groups in West Papua have been engaged in a decades-long struggle for independence from Indonesia, with reports of increasing violence and human rights violations within the territory.
e adamant that they respect Indonesian sovereignty over West Papua, although successive governments in Port Moresby have also raised their concerns about human rights abuses and violent crackdowns.
Dr Joseph said unrest in West Papua risked spilling over the border.
"We pretty much respect whatever happens within Indonesian territory to be an internal Indonesian matter," Dr Joseph said.
"But if it comes into the PNG side of our territory, definitely it involves us."
He said PNG had proposed building a 10km buffer zone along the border, which would become a "no-man's land" that would be free from military infrastructure.
"And then we build joint patrol posts along the way so that both TNI (Indonesian National Armed Forces) and PNGDF (Papua New Guinea Defence Force) can man, and both sides can police that no-man's land together," he said.
"That's the sort of close collaboration we want to see."
