Prime Minister Shigeru Ishiba is facing criticism from within his own party over his last-minute decision to skip a NATO summit in the Netherlands, at a time when fostering ties with the military alliance is seen as vital to counter China's rise in the Indo-Pacific.

Ishiba's absence also gave rise to the view that he sought to avoid a situation in which Japan, a non-NATO member but close U.S. ally, would be pressed by U.S. President Donald Trump to spend more on its defense, as NATO leaders at the two-day meeting that ended Wednesday discussed substantially increasing defense spending.

Ishiba had planned to make a three-day trip from Tuesday to attend the summit. But the Japanese government canceled the trip only a day before he was due to leave for The Hague, citing "various circumstances."

It came after the United States notified other governments that Trump would not be attending a meeting between NATO and its Indo-Pacific partners known as the IP4 -- Japan, along with Australia, South Korea and New Zealand.

Ishiba's attendance would have made it the fourth straight year since 2022 that a sitting Japanese prime minister attended a NATO summit, underscoring the importance the country attaches to its deepening ties with the group, especially in the wake of Russia's war on Ukraine.

"I don't understand why he had to cancel the trip despite all the preparations that went into it," said a lawmaker of the Liberal Democratic Party, which Ishiba heads.

In his place, Japan sent Foreign Minister Takeshi Iwaya to the gathering, which South Korea's new President Lee Jae Myung and Australian Prime Minister Anthony Albanese likewise opted to skip.

Ishiba has repeatedly said the security of the Euro-Atlantic and that of the Indo-Pacific are inseparable as he stressed the need for more cooperation between Japan and NATO.

The military alliance, which has traditionally sought to respond to threats from Russia, has been expanding its outreach, acknowledging the challenges posed by China's growing military power in the Indo-Pacific.

In response to "profound" security challenges, NATO leaders agreed Wednesday to commit to investing 5 percent of gross domestic product annually for defense and security-related spending by 2035.

The agreement came when Japan is wary of further pressure from the Trump administration to increase defense outlays, despite already on course to boost related spending to 2 percent of GDP by fiscal 2027 in the face of an assertive China and North Korea's nuclear and missile development.

Japan's current military buildup plan marks a drastic change given its war-renouncing Constitution and its commitment to using force only for self-defense that has limited any substantial increases in spending for decades.

A Japan-U.S. diplomatic source had said earlier that the Trump administration presented a plan to the Japanese government to raise its defense spending to 3.5 percent of GDP. The request is believed to have prompted Tokyo to call off a planned high-level meeting of diplomats and defense officials in Washington, ahead of a national election.