US Defense Secretary Jim Mattis reviews the honour guard before a meeting with Japan's Defense Minister Tomomi Inada in Tokyo. Photo: Reuters/Toru Hanai

US Defense Secretary Jim Mattis wrapped up a visit to Japan on Saturday reaffirming Washington’s commitment to its defence treaty with Tokyo amid concerns about President Donald Trump’s approach to the region and the alliance.

Mattis reiterated that provocations by North Korea, which is advancing its nuclear weapons and missile programs, as well as China’s growing assertiveness in the South and East China Seas, left no room for doubt about US commitment to Japan’s defence.

That was similar to the message that Mattis – making his first overseas trip since taking office – delivered in South Korea, Washington’s other key Asian ally, earlier in the week.

He appeared eager to reassure Japan of US resolve, after a 2016 election campaign in which Trump suggested both South Korea and Japan were benefiting from a US security umbrella without sharing enough of the costs.

“The US-Japan alliance is critical to ensuring that this region remains safe and secure – not just now, but for years to come,” Mattis told a joint news conference with Japanese Defense Minister Tomomi Inada.

But in what could been seen as a subtle prod to Japan to do more, he added: “But make no mistake: in my meetings with Japanese leaders, both our nations recognise that we must not be found complacent in the face of the emerging challenges we face.

“As our alliance grows, it will be important for both our nations to continue investing in our defence personnel and capabilities.”

Mattis said Tokyo’s financial support for US troops in Japan had been a “model of cost-sharing,” while Inada told the same news conference there had been no discussion of whether Japan should increase that funding.

Mattis also noted that Prime Minister Shinzo Abe has increased defence spending since taking office in December 2012, a move he said was “on the right track.”

Japan’s defence spending is around 1% of gross domestic product, compared to around 2% for China and over 3% for the United States.

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