President Donald Trump has warned North Korea the United States is prepared to use the full range of its military power if needed to defend itself and its allies during a visit to South Korea that took him to heart of the nuclear standoff with Pyongyang.
Speaking at a joint news conference with South Korean President Moon Jae-in, Mr Trump said that while he hopes to use all tools short of military force, he was prepared to do whatever was necessary "to prevent the North Korean dictator from threatening lives ... so needlessly."
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"We cannot allow North Korea to threaten all that we have built," Mr Trump said on the first day of a two-day visit to South Korea.
But at times taking a less strident tone, Mr Trump also urged North Korea to "do the right thing" and said: "I do see some movement" - though he declined to elaborate.
"We hope to God we don't have to use" the United States' full military capabilities, he said.
Landing earlier at Osan Air Base outside Seoul, the president and First Lady Melania Trump stepped down from Air Force One onto a red carpet as he began a visit that could aggravate tensions with North Korea.
He then flew by helicopter to Camp Humphreys, the largest US military base in the country, and met US and South Korean troops, along with Mr Moon.
The White House says Mr Trump's trip is intended to demonstrate US resolve over his hardline approach to the North Korean nuclear and missile threats, but many in the region fear further bellicose presidential rhetoric could increase the potential for a devastating military conflict on the Korean peninsula.
Meeting with military commanders about the North Korea issue, Mr Trump told reporters: "Ultimately it will all work out, it always works out, it has to work out." He did not elaborate.
Mr Trump praised president Moon, hailing him for "great cooperation" despite differences over how to confront North Korea and over a trade pact between the United States and South Korea.
When the two leaders later held formal talks after an elaborate welcoming ceremony outside the presidential Blue House in Seoul, Mr Moon told Mr Trump he hoped his visit would relieve some of South Koreans' anxiety over North Korea and serve as a "turning point in resolving the North Korean nuclear issue".
Three U.S. aircraft carrier strike groups will exercise together in the Western Pacific in the coming days in a show of force rarely seen in the region, US officials said.
On the second leg of his five-nation trip, Mr Trump toured the sprawling Camp Humphreys garrison, which lies about 100 km from the border with reclusive North Korea.
Mr Trump was greeted with applause and a few cheers as he and Mr Moon entered the mess hall at lunch hour.