Papua New Guinea signed a defence pact with the United States on Monday, giving US forces access to its airfields and ports as Washington vies with China's expanding footprint in the Pacific region.
Washington has growing concerns about China's rise in the Pacific, where it is trying to woo nations with an array of diplomatic and financial incentives in return for strategic support.
Defence Minister Win Bakri Daki inked the deal with US Secretary of State Antony Blinken before the start of a US meeting with the leaders of 14 South Pacific island states in the capital Port Moresby.
"A defence cooperation agreement is done," Prime Minister James Marape said at the signing ceremony, adding that the Pacific island was "elevating" its relationship with the United States.
Blinken said each of the two nations would be able to board the other's vessels, share technical expertise and "better patrol" the seas together.
"We are working together to shape the future. We are very much looking forward to taking our partnership to the next level," he said. In a sign of the intensifying rivalry over the South Pacific, Blinken was not alone in representing major powers aiming to counter Beijing's growing economic, political and military presence.
Indian Prime Minister Narendra Modi flew into town just hours before him on the eve of his own summit, asserting his nation's role as a regional power in the face of China's rise.
"We share your belief in multilateralism. We support a free, open, and inclusive Indo-Pacific. We respect the sovereignty and integrity of all countries," Modi told Pacific leaders in a separate summit.
By signing the security deal with PNG, Blinken will also expand the US military's capacity to deploy in the region.
Also Read | Modi stresses on boosting India-Papua New Guinea ties in talks with PM Marape, Governor-General Dadae
Beijing has snapped up mines and ports across the Pacific and last year inked a secretive security pact with the Solomon Islands that allows China to deploy troops to the country.
The United States fears that a Chinese military foothold in the South Pacific could outflank its facilities on Guam, and make the defence of Taiwan more complicated in the event of a Chinese invasion.
The State Department said the pact with PNG would "enhance security cooperation and further strengthen our bilateral relationship, improve the capacity of the PNG Defence Force, and increase stability and security in the region".
"Port Moresby is no longer the sleepy diplomatic outpost it once was," said Gordon Peake, a senior adviser for the Pacific Islands at the United States Institute of Peace.
"While China might not be mentioned anywhere in the document, it's an important subtext in this story of deepening US-PNG relations."
Marape last week said the deal would offer Washington movement in the country's waters in return for access to US satellite surveillance to battle "illegal activities on the high sea".
The deal would not prevent him from signing similar agreements with other nations, including China, he said.
China on Friday said it opposes the "introduction of any geopolitical games into the Pacific Island country region," without specifically referring to the deal or Blinken's visit.
The agreement has also prompted student protests at several universities, PNG's biggest newspaper the Post Courier reported, over fears it gives US forces too much autonomy at some of the country's key entry points.
Security was high in the capital on Monday, with roads blocked and bomb squad cars stationed around its downtown beach area close to where the leaders were meeting. Officers were also patrolling nearby waters on speedboats and jet skis.
Blinken replaced Joe Biden at the summit after the US president cancelled the trip to take part in debt ceiling talks in Washington.
On top of the deal, the US pledged to PNG $45 million in funding to tackle organised crime, climate change and HIV/AIDS, as well as protective equipment for its military, the State Department said.
Commander of the US Indo-Pacific Command, Admiral John Aquino, also visited a barracks in Oro Province on Monday where he was met by a military parade, the Courier reported.