U.S. President Donald Trump said on Sunday he had instructed the Pentagon to substantially reduce joint military exercises with South Korea.

"I am not happy with the fact that the United States has, long ago, agreed to participate in Joint Military Exercises with South Korea," Trump wrote in a post on Truth Social.

"These exercises are not only costly, with much of these costs paid for by the United States of America (as usual!), but send a signal that is totally inappropriate and hostile," he said.

"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 said.

The U.S. president also mentioned Seoul's refusal to join U.S. actions to "denuclearize" Iran.