Australia and Papua New Guinea's military forces will become "totally integrated" as part of a landmark defence treaty between the two nations, the ABC can reveal.

The major security agreement is expected to be signed on Monday, the day before Papua New Guinea marks 50 years of independence.

Australian Prime Minister Anthony Albanese, Defence Minister Richard Marles, Foreign Minister Penny Wong and Minister for the Pacific Pat Conroy are due to arrive in Papua New Guinea on Monday ahead of the celebrations.

PNG's Defence Minister Billy Joseph said the deal was a "mutual defence treaty" that would see the countries work together to defend each other's territories.

"We're not talking about interoperability, we're talking about totally integrated forces," he told the ABC.

"Australian Def

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