President Donald Trump's defense secretary is expected to underscore U.S. security commitments to key allies South Korea and Japan on his debut trip to Asia this week as concerns mount over North Korea's missile program and tensions with China.

Axar.az reports citing Reuters.

The trip is the first for retired Marine General James Mattis since becoming Trump's Pentagon chief and is also the first foreign trip by any of Trump's cabinet secretaries.

Officials say the fact that Mattis is first heading to Asia - as opposed to perhaps visiting troops in Iraq or Afghanistan - is meant to reaffirm ties with two Asian allies hosting nearly 80,000 American troops and the importance of the region overall.

That U.S. reaffirmation could be critical after Trump appeared to question the cost of such U.S. alliances during the election campaign. He also jolted the region by pulling Washington out of an Asia-Pacific trade deal that Japan had championed.

"It's a reassurance message," said one Trump administration official, speaking on condition of anonymity.

"This is for all of the people who were concerned during the campaign that then-candidate, now-president, Trump was skeptical of our alliances and was somehow going to retreat from our traditional leadership role in the region."

Trump himself has spoken with the leaders of both Japan and South Korea in recent days and will host Japanese Prime Minister Shinzo Abe in Washington on Feb. 10.

Mattis leaves the United States on Feb. 1, heading first to Seoul before continuing to Tokyo on Feb. 3.