The United States says a visit to Papua New Guinea last week was part of its commitment to a "free and open Indo-Pacific".
Vice President Mike Pence attended the APEC summit in Port Moresby, where the US and China clashed openly over trade disputes and influence in the region.
The US has pumped more than $US1.8 billion into the Indo-Pacific this year, although it's unclear how much of this was destined for Pacific Islands.
At APEC, the US announced a new economic assistance program with initial funding of $US9 million for APEC economies.
In a statement, a State Department spokesperson said this would promote fair and free trade and opportunities for US businesses in the region.
The US was also expanding maritime security, humanitarian assistance and disaster relief and peacekeeping to the Pacific Islands, the spokesperson added.
At APEC, the US, PNG, Australia, New Zealand and Japan announced a five-nation partnership with the goal of supporting expanding electricity access to 70 percent of PNG's population by 2030.
During the summit, the US also said it would join Australia in developing a naval base in PNG, in an apparent move to curb China's growing influence.
Pence makes Guam visit
On Sunday, Mr Pence visited Guam, meeting with the outgoing Governor Eddie Calvo and American military service members in the country.
Post Guam reported the two discussed issues including oustanding reimbursements for Medicaid in Guam worth millions of dollars.