The United States will join Australia in expanding the Lombrum Naval Base on Papua New Guinea's Manus Island.
US vice-president Mike Pence made the announcement today at the APEC leader's summit in PNG's capital Port Moresby.
Mr Pence, who is representing his country at APEC in the absense of President Donald Trump, used his speech today to assert US partnership with Pacific Islands and other allies in the wider region.
Without elaborating on details, he confirmed the US would partner with Papua New Guinea and Australia on a joint naval base on PNG's northern island.
This builds on the plan to re-develop Manus' Lombrum site as a base for Australian vessels, and joint acivities with PNG, including maritime patrolling, as revealed by Canberra and Port Moresby in recent weeks.
The plan could yet face a challenge as the Manus Governor warned he could obstruct the naval base project if his province wasn't consulted properly.
Mr Pence delivered strong criticism of China on trade, its advances in the South China Sea, and its development assistance in the Pacific.
"We don't drown our partners in a sea of debt. We don't coerce or compromise your independence," he said of China's Belt and Road infrastructure development initiative.
Earlier, Chinese President Xi Jinping took a swipe at the US as he espoused the merits of free trade during his APEC speech.
He described US protectionism and unilateralism as a defeatest approach bound for failure, and defended China's development initiatives in developing economies.
Xi arrived in PNG two days before the summit and gained much of the APEC spotlight before other world leaders arrived, although
Presiding over the opening of major Chinese-built projects such as a new six-land road in Moresby, Xi has been feted by PNG's leadership.
"No one should stop developing countries from pursuing a better life," Xi said.
"We should strengthen development co-operation and help developing countries eliminate poverty."
Australia's Prime Minister Scott Morrison also spoke at the summit in support of free trade, saying trade wars were in no country's interest.
Mr Morrison played down suggestions that American buy-in on the Manus plan was a bid to edge out China's influence in the region, emphasising that it was PNG's initiative.
"This is a strong partnership designed to make a stronger Pacific, a more prosperous Pacific. For Australia, this is our family of nations that we work with here in the Pacific and we'll be there very much as an equal family member," he said.
Mr Pence said the US was committed to Pacific Islands region "as never before, by investing in infrastructure, co-operating on fisheries, and signing new maritime treaties".
"Even the smallest nations are equal stakeholders in a free and open Indo-Pacific, and we are proud to stand and partner with all of them."
Both the US and China are to announce new development packages for the Pacific region during the summit.
President Xi has already held a meeting in PNG with Pacific Island leaders who were invited to APEC as observers.
However local and international media were barred from attending the Chinese leader's meeting with Pacific leaders.
Despite being accredited and invited to cover the event, Chinese officials blocked access to all media apart from those from China's state-run agencies.