President Donald Trump's "America first" approach to foreign policy is "alarming," Caroline Kennedy, who recently resigned her post as U.S. ambassador to Japan, said Friday morning.

"To be taken for granted, or to be insulted as an ally who has fought alongside the United States for example, with Australia, or who contributes a huge amount to American security, in the case of Japan and Korea, is alarming," Kennedy told NBC's "Today" anchor Matt Lauer in an exclusive interview.

"I think that, hopefully, the president will realize the benefits of working with our friends and allies around the region."

Kennedy resigned her post in January. She had been ambassador to Japan for three years, after her appointment by President Barack Obama.

Her comments came after Defense Secretary James Mattis arrived Friday morning in Japan, in a trip planned to reassure the nation's leaders that the United States will continue as an ally, a status that came under concern following tough talk by Trump during his 2016 presidential campaign.

At that time, Trump made a promise that he would force Japan, as well as other Asian countries, to foot more of the costs to defend their country.

Japan not only contributes more for defense than any other country, said Kennedy, pushing back at the idea to force the key U.S. ally to spend more.

"They contribute more than 75 percent of the cost of the bases," Kennedy said. "It's in our interest that Japan be strong and that our troops be there. That makes us safer here at home."

Kennedy on Friday commended Mattis' visit, saying that the region is "critical to our future, so it's important that the defense secretary went to consult and reassure our allies about our commitment."

Japan is the United States "number one ally" in the Asian region, and remains one of its most strategic partners, said Kennedy, and a safe Japan helps U.S. security.

The country's continued security also means "jobs and a lot of economic opportunities for American companies," Kennedy told Lauer.

There has been some talk that Kennedy, the daughter of late President John Fitzgerald Kennedy, would continue her family's political legacy by running for political office, but she said Friday she is "looking to figure what I'll do next," while joking that she thinks she'd "rather be on morning TV" than run for public office.