US Defence Secretary James Mattis will seek to reassure allies worldwide they can still rely on an increasingly inward-focused US, as he heads to East Asia on the first overseas trip by a Trump administration cabinet member.

The retired Marine Corps general leaves on Wednesday for South Korea and Japan — two of the US’s closest allies — amid questions about President Donald Trump’s commitment to the region, having pulled out of a 12-nation Pacific trade deal and suggesting previously that Asian nations weren’t paying enough for US troops stationed in their countries.

Questions over ties with Tokyo and Seoul come against the backdrop of an increasingly belligerent regime in North Korea under Kim Jong-un. Pyongyang appears to be making preparations for another nuclear or missile test and has been advancing its weapons capability, with Trump saying he would not allow North Korea to threaten US soil.

The trip will reverberate beyond those two key northeast Asian allies, said Patrick Cronin, senior director of the Asia-Pacific Security Program at the Center for a New American Security in Washington. “It’s still very important to reassure allies at the time when there’s so much uncertainty, turbulence, unpredictability,” he said.

While the Pentagon downplayed expectations of any immediate shift in the US military’s approach toward the region or in its presence, Trump’s style could throw doubt on assurances offered during the visit, according to Yoichi Kato, a senior research fellow at the Rebuild Japan Initiative Foundation in Tokyo.

“There is so much unknown and unpredictable in the Trump administration that it is hard to judge how far comments made by Secretary Mattis will be reflected in Donald Trump’s policy,” Kato said. “Trust in the US as an alliance partner has already been damaged to some extent and Mattis’s most important job on this trip will be to erase that kind of doubt.”

South Korea hosts about 28,500 US troops while Japan has 50,000.

Mattis “wants to find out what their concerns are, learn more about the issues that we face together and prepare to address those,” Pentagon spokesman Jeff Davis said. “He’s primarily in listening mode right now.” He said: “The intent of this is not to roll out any big change in US policy.”

Nevertheless, Mattis’s trip will be “high-level signalling” to key allies, Cronin said.

South Korea, the first stop, is facing turbulence after President Park Geun-hye was impeached over an influence-peddling scandal. Acting President Hwang Kyo-ahn spoke to Trump by phone on January 29, with the American president reiterating the US’s “ironclad commitment to defend” it against North Korea. Trump said the alliance will be “better than ever before,” according to a statement on the call from Hwang’s office.

In addition to discussing joint defence capabilities, Mattis will meet with South Korean Foreign Minister Yun Byung-se to discuss North Korea.

By sending Mattis to South Korea first, Trump is delivering a message the US will preserve its alliance and sending a warning to Pyongyang, said Baek Seung-joo, a former deputy defence minister who’s a lawmaker with the ruling Saenuri party. The trip also sends indirect signals to China that the US stands by a plan approved during the Obama administration to deploy in South Korea an antimissile system known as Thaad, which Beijing opposes, Baek said.

“His visit will clarify and kill some blurry areas and extreme talks that have been hovering around before the start of the Trump administration,” Baek said. “While Obama excluded chances of any military actions against the North, I think Trump will leave such chances, including a surgical strike, ambiguous.”

US allies and adversaries will also be watching for more direct signals toward Beijing. Trump has stoked fears of a trade war by threatening to label China a currency manipulator and weighing tariffs on Chinese goods. Meanwhile, Trump’s choice for secretary of state, Rex Tillerson, suggested during a confirmation hearing that the US would toughen its stance over China’s island-building efforts in the disputed South China Sea.

Mattis’s visit to Japan comes ahead of a February 10 meeting in Washington between Japanese Prime Minister Shinzo Abe and Trump, the second between the leaders since his election win. The US-Japan alliance, a bedrock of security in the Pacific region, has come under stress since Trump backed out of the Trans-Pacific Partnership trade accord shortly after taking office. Abe, a key advocate of the deal, has indicated he’s open to bilateral trade talks between the US and Japan.

“I want to hold frank discussions with Secretary Mattis about various issues and to make it a meeting that contributes to deepening and strengthening the alliance and making it unshakeable,” Japanese Defence Minister Tomomi Inada told parliament this week.

Japan will also be seeking assurances Trump will hold to the Obama administration’s pledge to come to its defence if needed over islands in the East China Sea that are in dispute with China. China regularly sends planes and ships near the area, leading Japan to scramble fighter jets.

Some in Japan are worried about whether Trump will act on his campaign rhetoric about US troops in the region, according to Itsunori Onodera, a former Japanese defence minister.

“There is concern among a section of the Japanese people because he has said that protecting allies, including Japan, costs a great deal of money,” Onodera said. “We need to get things ready so that we are not in a panic if America’s thinking suddenly changes.”