Secretary of State Rex Tillerson warned Friday that military action against North Korea was "on the table" if the country continued to develop its weapons program.
"If they elevate the threat of their weapons program to a level that we believe requires action then that option is on the table," he told a press conference in South Korea.
"Certainly we do not want for things to get to a military conflict," he added. "But obviously if North Korea takes actions that threaten the South Korean forces or our own forces then that would be met with an appropriate response."
North Korea carried out two nuclear tests last year, and in January a senior North Korean official told NBC News that the country was ready to test-fire an intercontinental ballistic missile "at any time, at any place."
Tillerson's comments came during his first official visit to Asia as President Donald Trump's secretary of state.
A day earlier in Tokyo, he said that two decades of bipartisan diplomatic efforts toward Kim Jong Un's regime had failed.
"Let me be very clear — the policy of strategic patience has ended," he added on Friday. "We are exploring a new range of security and diplomatic measures. All options are on the table."
"Warfighting in North Korea would be hard"
Tillerson said that the U.S. has provided $1.3 billion in assistance to the authoritarian regime since 1995, but "in return North Korea has detonated nuclear weapons and dramatically increased its launches of ballistic missiles to threaten America and our allies."
However, he added that "we have many, many steps we can take before we get to" military action and "we hope that that will persuade North Korea to take a different course of action. That's our desire."
In addition to its two nuclear tests last year, the North has carried out numerous missile launches and says it's working on a nuclear-tipped missile that can reach America.
"Today, North Korea not only threatens its regional neighbors but the United States and other countries," Tillerson added.
Despite mooting the possibility of conflict, Tillerson said Thursday that "North Korea and its people need not fear the United States or their neighbors in the region, who seek only to live in peace in the region."
Tillerson also visited the volatile Demilitarized Zone that divides the two rival Koreas on Friday, with his entourage standing on the South side just three feet away from North Korean soldiers on their side of the line.
North Korea has amassed one of the largest standing armies in the world and spends an estimated quarter of its gross domestic product on its military.
If conflict ever were to flare, "warfighting in North Korea would be hard," according to Maj. ML Cavanaugh, a U.S. Army strategist writing for the Modern War Institute at West Point, which is a research center of the United States Military Academy.
In an article posted Tuesday, Cavanaugh warned of North Korea's tough, "Afghanistan-like geography" and an army that could act like "a much better-trained, much better-armed version of the Taliban."