FUSSA, Japan — President Donald Trump praised Japan as a “crucial ally” and warned adversaries not to test America’s resolve Sunday as he opened a grueling and consequential first trip to Asia.

Trump landed at Yokota Air Base on the outskirts of Tokyo and was greeted by cheering service members. Trump then donned a bomber jacket for a speech in which he touted American firepower and the U.S. alliance with Japan.

“Japan is a treasured partner and crucial ally of the United States and today we thank them for welcoming us and for decades of wonderful friendship between our two nations,” he said, speaking in front of an American flag inside an airplane hangar.

Trump was expected to spend much of his 12-day, five-country Asian tour exhorting allies and rivals to step up efforts to counter the dangers posed by North Korea, which continues to move forward with its nuclear weapons program. Trump and North Korean leader Kim Jong Un have been engaged in an escalating war of words, with Trump repeatedly referring to Un as “Little Rocket Man” and threatening in a recent speech to “totally destroy” the nation, if necessary.

Even before he landed, Trump used the first moments of the trip to denounce the North as “a big problem” that must “be solved.”

“There’s been 25 years of total weakness, so we are taking a very much different approach” toward the North, he told reporters traveling with him.

During the speech, Trump did not mention North Korea by name, but warned of the consequences of crossing what he called the “most fearsome fighting force in the history of our world.”

“Together with our allies, America’s warriors are prepared to defend our nation using the full range of our unmatched capabilities. No one — no dictator, no regime and no nation — should underestimate, ever, American resolve,” Trump told the troops.

Some regional analysts have speculated that Trump’s presence in Asia may prompt North Korea to take provocative action, like another missile test.  Trump, when asked about that possibility aboard Air Force One, said “we’ll soon find out.”