US President Donald Trump ordered the Pentagon on Sunday to scale back planned joint military exercises with South Korea after the Republican president said South Korea declined to help denuclearise Iran.

Trump said in a social media post that the exercises scheduled 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 strengthen readiness against North Korean threats.

US and South Korean forces were expected to practice joint operations in complex situations, 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”.