Washington (CNN) Secretary of Defense James Mattis will make his first official trip abroad next week, traveling to Japan and South Korea -- visits that could help shore up allies and send a message to China.

The four-day trip beginning next Wednesday will "underscore the commitment of the United States to our enduring alliances," said US Navy Capt. Jeff Davis, who called South Korea and Japan "two critical US allies,"

His visit to two of America's long-time treaty allies, where Mattis will meet with his defense counterparts in each country, comes amid questions surrounding President Donald Trump's commitment to those alliances.

Trump had voiced a skeptical view of America's relationships with Japan and South Korea during the 2016 campaign, saying Tokyo and Seoul should pay more for the thousands of American troops stationed in both countries.

There are approximately 50,000 US troops in Japan and about 28,000 in South Korea.

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