The United States says it intends to play a "more limited" role in deterring nuclear-powered North Korea, shifting the burden of responsibility onto South Korea.
The change of strategy came in a Pentagon policy document released on Friday, in a move likely to raise concerns in Seoul.
Earlier this month, North Korean leader Kim Jong Un approved the launching of multiple ballistic missiles toward its eastern waters.
South Korea hosts about 28,500 US troops in combined defence against North Korea's military threat, with Seoul raising its defence budget by 7.5 per cent for this year.
"South Korea is capable of taking primary responsibility for deterring North Korea with critical but more limited US support," said the National Defense Strategy, a document that guides the Pentagon's policies.
"This shift in the balance of responsibility is consistent with America's interest in updating US force posture on the Korean Peninsula."
In recent years, some US officials have signalled a desire to make US forces in South Korea more flexible to potentially operate outside the Korean Peninsula.
That would be in response to a broader range of threats, such as defending Taiwan and checking China's growing military reach.
Even though it has resisted the idea of shifting the role of US troops, South Korea has worked to grow its own defence capabilities over the past 20 years.
On a visit to Seoul last November, US Defense Secretary Pete Hegseth praised South Korea's plans to increase its military spending.
With a current troop strength of about 450,000, Seoul has the goal of being able to take on a war-time command of the combined US-South Korean forces.
The wide-ranging document, which each new administration publishes, said the Pentagon's priority was defending the homeland.
In the Indo-Pacific region, the document said, the Pentagon was focused on ensuring that China could not dominate the United States or US allies.
"This does not require regime change or some other existential struggle," the document said.
"Rather, a decent peace, on terms favourable to Americans but that China can also accept and live under, is possible."
Noticeably, the 25-page document did not mention Taiwan by name.
China claims democratically governed Taiwan as its own territory and has not ruled out the use of force to take control of the island.
Taiwan rejects Beijing's sovereignty claims and says only the people of Taiwan can decide its future.
Donald Trump and Kim Jong Un met three times during the US president's first term, but Pyongyang has not directly responded to renewed calls from Washington to resume dialogue.
During a visit to the US by South Korea Prime Minister Kim Min-seok, he discussed with US Vice-President JD Vance how Washington could improve ties with North Korea.
Mr Kim suggested that Mr Trump consider sending a special envoy to Pyongyang, Yonhap news and other media said.
The Korean War ended in 1953 with an armistice, not a peace treaty, halting active fighting but leaving the conflict legally unresolved.
As a result, North and South Korea remain technically at war, separated by the heavily fortified Demilitarised Zone.
Reuters/ABC
