U.S. Defense Secretary Pete Hegseth attended on Saturday a war memorial service on Iwoto Island in the Pacific as he kicked off his first official visit to Japan, showcasing the alliance between the two countries that were enemies 80 years ago.

Hegseth is on his first trip to Asia, and the visit is part of U.S. efforts to work toward "a free and open Indo-Pacific," according to the Defense Department.

But concerns linger that the administration of President Donald Trump could strain the alliance by pressing Japan to increase its spending on defense amid China's assertiveness and North Korea's nuclear and missile threats.

On Iwoto Island, the site of a fierce battle between Japan and the United States in the closing stages of World War II, Hegseth joined Japanese Prime Minister Shigeru Ishiba and Defense Minister Gen Nakatani for the ceremony marking the 80th anniversary of the Battle of Iwojima.

"Our alliance has been and remains the cornerstone of freedom, prosperity, security and peace in the Indo-Pacific, and it will continue," Hegseth told the event, stressing the importance Trump's administration places on relations.

The alliance shows "how yesterday's enemy has become today's friend," Hegseth said. "Our unity and our shared purpose is what strengthens us."

He laid a wreath at a cenotaph for war victims with other senior U.S. officials.

"We must never forget that the peace and prosperity we enjoy today was built on the precious sacrifice of the war dead and untiring efforts by people over the 80 years since the war ended," Ishiba said at the ceremony, pledging to "elevate the alliance to new heights."

The Battle of Iwojima lasted for about a month from when U.S. forces landed in February 1945, with around 21,900 Japanese and 7,000 U.S. soldiers estimated to have been killed. The island was returned to Japanese sovereignty in 1968.

On Sunday, Hegseth will hold a meeting with Nakatani in Tokyo to discuss measures to beef up the alliance's deterrence. He will also hold talks with Ishiba the same day.

Just days before, Japan launched a new command for the Self-Defense Forces to better integrate its ground, maritime and air defenses, in a major revamp aimed at ensuring smoother coordination with the U.S. military at a time when tensions are heightened over potential contingencies involving Taiwan.

Under Trump's predecessor Joe Biden, the U.S. government decided to upgrade U.S. Forces Japan, which will serve as a key counterpart for the SDF Joint Operations Command.

However, recent U.S. media reports have said that the Pentagon is considering halting the planned expansion of USFJ as part of cost-cutting efforts.

Hegseth could call on Japan to ramp up its defense budget, even though the Asian nation decided in 2022 to increase related spending to 2 percent of its gross domestic product by fiscal 2027 in a significant shift in its postwar security policy under its war-renouncing Constitution.

Hegseth's trip began Monday and has included stopovers in Hawaii, Guam and the Philippines, another key U.S. ally in Asia.

During the trip, he has been dogged by questions about a scandal related to the sharing of highly sensitive attack plans with a journalist on a commercial messaging app. He and other high-ranking Trump administration officials have faced criticism for their roles in the security breach.