The United States and South Korea have agreed to shorten their annual Ulchi Freedom Shield exercise and reduce some joint field training after President Donald Trump ordered a substantial reduction in the drills.

South Korea's military said the exercise would end on Friday rather than 27 August. It said the allies had agreed to adjust the duration and scale at the request of the United States and would downsize some field training events.

The Pentagon said it was continuing training that enhances tactical capability, with some events cancelled or converted to simulations. It said the adjustments would preserve essential readiness and training objectives.

The decision is likely to sharpen an old alliance debate. The drills are a pillar of US-South Korean deterrence, but are also routinely denounced by North Korea, which portrays them as rehearsal for invasion.