Blinken and Indian Prime Minister Narendra Modi held separate meetings with 14 Pacific island leaders in the PNG capital Port Moresby, pledging support for the region's priorities of health, development and climate change.

The United States and its allies are seeking to deter Pacific island nations from forming security ties with China, a rising concern amid tension over Taiwan, and after Beijing signed a security pact with Solomon Islands.

Pacific island leaders, whose territories span 40 million square km (15 million square miles) of ocean, have said rising sea levels caused by climate change are their most pressing security priority.

Blinken told PNG Prime Minister James Marape that Washington would deepen its partnership across the board with PNG, and that he expected partnerships with U.S. businesses would bring tens of billions of dollars' worth of new investment.

After university students protested against the defence agreement on Monday, Marape told a joint news conference with Blinken "there is nothing for us to be fearful about".

The accord updated an existing U.S. military relationship, he said, and "has nothing to do with China".

"We have a healthy relationship with the Chinese government and they are an important trading partner," Marape said.

Marape said on Sunday the defence agreement would see an increase in the U.S. military presence over the next decade, while the U.S. State Department said it would bolster regional security.

"The defence cooperation was drafted by the United States and Papua New Guinea as equals and sovereign partners," Blinken said at a signing ceremony.

It will expand PNG defence capacity to enhance humanitarian assistance and disaster response, and make it easy for U.S. and PNG forces to train together, Blinken said.

In Beijing, Chinese foreign ministry spokesperson Mao Ning said China had no objection to mutually beneficial cooperation with Pacific island countries such as PNG, but added: "What we need to be vigilant about is engaging in geopolitical games in the name of cooperation, and we also believe that no cooperation should target any third parties."

'KNOW WHAT IS HAPPENING'

The U.S. and PNG struck a separate agreement on increasing surveillance of PNG's exclusive economic zone through U.S. Coast Guard patrols, protecting its economy from illegal fishing.

The United States will provide $45 million in new funds as it works with PNG to strengthen economic and security cooperation, including protective equipment for the PNG defence force, climate change mitigation and tackling transnational crime and HIV/AIDS, Blinken said.

Blinken headed the U.S. delegation in PNG instead of President Joe Biden, who cut short an Asia trip to deal with the U.S. debt-ceiling crisis.

Addressing the 14 Pacific island leaders, Blinken said he was carrying an invitation from Biden for them to return to Washington in the autumn for a second summit following an inaugural meeting hosted by the White House last year.

Modi told the Forum for India-Pacific Islands Cooperation that India would be a reliable development partner and was committed to a "free, open and inclusive Indo Pacific".

"We are willing to share our capabilities and experiences in digital technology, space technology, health security, food security, climate change and environment protection," he said.

The Quad leaders of Australia, United States, Japan and India had agreed in Japan at the weekend to increase cooperation with the Pacific, Modi said.

In PNG, the United States also signed a renewed strategic agreement with Palau, known as a Compact of Free Association (COFA), and will sign another with Micronesia on Tuesday, under which the U.S. is responsible for the nations' defense and gains continued access to huge swathes of the Pacific.

Blinken said Washington looked forward to entering negotiations on a third COFA, with the Marshall Islands, "very soon" and said that under the three compacts the U.S. would commit $7.1 billion over 20 years.

Biden's COFA negotiator Joseph Yun told Reuters on Saturday he hoped to finalise a deal with the Marshall Islands in the coming weeks.