Trump wrote on Truth Social that the exercises slated to begin this week are costly and "send a signal that is totally inappropriate and hostile" to North Korea, which he said "has been unthreatening and respectful" while Trump has been in the White House.
"Therefore, and based on the fact that it is too late to cancel, I have instructed Secretary of War, Pete Hegseth, to substantially reduce the Joint Military Exercises!" Trump wrote.
The 11 days of exercises involving 18,000 South Korean soldiers were designed to beef up readiness against North Korean threats.
US and South Korean forces were expected to practice joint operations in complex scenarios, including a live-fire exercise to test joint precision targeting and manoeuvre, a wet gap crossing, and distribution of pre-positioned military equipment, according to the US military.
A day earlier, Trump posted a photo of himself standing next to North Korea's Kim Jong-un, writing that the two leaders get along great "despite the unfriendly look on this particular picture".
North Korea's Foreign Ministry has called the US-South Korean training "a rehearsal for an aggressive war" that is triggering a different level of instability in the region.
Trump met with the reclusive North Korean leader three times during his first term to discuss the country's nuclear program, most recently in 2019. Since returning to office, Trump has expressed interest in continuing those discussions.
This is not the first time Trump has sought to end the exercises. During his first term he also issued a surprise announcement that called the wargames "provocative".
"We will be stopping the war games, which will save us a tremendous amount of money, unless and until we see the future negotiation is not going along like it should," Trump told reporters after his 2018 meeting with Kim in Singapore.
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