The US says the deal with enhance security cooperation and further strengthen the two countries’ bilateral relationship.

PNG, just north of Australia, is strategically significant and was the site of fierce battles during World War II.

The US State Department said the Defence Cooperation Agreement 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”.

PNG Prime Minister James Marape said the deal would help his country face significant challenges.

“We have our internal security as well as our sovereignty security issues,” Marape said on Monday morning. “We are stepping up on that front to make sure our borders are secure.”

Last week he said the deal would provide PNG with access to US satellite surveillance to battle “illegal activities on the high sea”.

There were protests at several university campuses, including in Lae, the country’s second-biggest city, against signing the agreement amid concern about the effect on the country’s relationship with China, an important trade partner.

There are also concerns about the militarisation of the Pacific after Beijing signed a security agreement with the Solomon Islands last year. That pact has led the US to renew its commitment to the region, opening new embassies and hosting an unprecedented summit of Pacific leaders at the White House.

After signing the defence agreement, US Secretary of State Antony Blinken will follow Indian Prime Minister Narendra Modi in holding separate talks with 14 Pacific leaders, including New Zealand Prime Minister Chris Hipkins, who have gathered in the PNG capital Port Moresby.

Police Commissioner David Manning said there was a heavy police and military presence around the capital with roads blocked and defence patrol boats in the water around the meeting venue.

US President Joe Biden was supposed to travel to PNG but cancelled the trip to take part in debt ceiling talks in Washington. He would have been the first sitting president to visit the country.

While the US defence pact is being framed as a deal to protect Papua New Guinea’s territorial borders, experts say China’s Pacific presence is a key driver.

“Port Moresby is no longer the sleepy diplomatic outpost it once was,” Gordon Peake, a senior adviser for the Pacific Islands at the United States Institute of Peace, told the AFP news agency.

“While China might not be mentioned anywhere in the document, it’s an important subtext in this story of deepening US-PNG relations.”

Marape said the deal would not prevent him from signing similar deals with other nations, including China.

India’s Prime Minister Narendra Modi is also in PNG to meet Pacific leaders.

Modi told the 14 leaders of the Forum for India-Pacific Islands Cooperation that India would be a reliable partner to small island states amid difficulties caused by supply chain disruptions and climate change.

He stressed that India was committed to a free and open Indo-Pacific.