South Korea and the United States are expected to suspend their massive wintertime joint Air Force exercise, Vigilant Ace, usually held in December, for the second year in a row to support diplomacy for the denuclearization of the Korean Peninsula, sources said Sunday.

Instead of the combined exercise, the South Korean and U.S. militaries will stage separate air drills.

"South Korea and the United States are closely coordinating the details of each exercise to ensure combined military readiness," an official with the Republic of Korea Air Force said, adding details of such drills were not open to the public.