A senior US official has stressed that the upcoming three-way summit involving the United States, Japan and South Korea will serve as an important opportunity to enhance their trilateral relationship.

White House National Security Council spokesperson John Kirby spoke in an interview with NHK on Thursday prior to the summit scheduled near Washington the next day.

Kirby said President Joe Biden "has focused very, very keenly on the Indo-Pacific since Day One" of his administration.

He said the summit is a "culmination" of a couple of years' effort by the president to prioritize the Indo-Pacific and more specifically, US ties with Japan and South Korea.

The spokesperson said President Biden is "very personally attached to making sure that" the relationship among the three countries continues to improve and their cooperation keeps deepening.

He added that the president is personally invested in making sure the summit will produce "real tangible results and initiatives that will be able to be sustained over the long term."

Kirby was also asked about Washington's extended deterrence, which refers to its commitment to defend its allies with nuclear weapons and other capabilities.

He said the US is "interested in improved trilateral coordination and communication on all things deterrence, including strategic deterrence."