SINGAPORE - US Defence Secretary Jim Mattis and his South Korean counterpart Jeong Kyeong-doo have cancelled the "Vigilant Ace" military exercise that was slated for December, a Pentagon spokeswoman said Friday.

The two officials agreed to suspend the drill to "give the diplomatic process" with Pyongyang "every opportunity to continue," spokeswoman Dana White said in a statement.

"Both ministers are committed to modifying training exercises to ensure the readiness of our forces," the statement read, saying the need for future exercises would continue to be evaluated.

The decision came as Mattis met with Jeong and South Japanese Minister of Defence Takeshi Iwaya on Friday at a security summit in Singapore.

White's statement said Iwaya was "consulted" on the matter. Mattis did not mention the decision when he spoke to reporters after his meetings with Jeong and Iwaya.

Following US President Trump's June meeting with North Korean leader Kim Jong Un, the United States said it would suspend "select" exercises with South Korea , including the large-scale Ulchi Freedom Guardian exercises scheduled for August.

Vigilant Ace is an air exercise aimed at improving coordination between the two armies that takes place every year in early December in South Korea .

Last year, 230 aircraft and some 12,000 US and South Korean troops participated.

In August Mattis had said the Pentagon would "see how the negotiations go, and then we will calculate the future, how we go forward."

US and South Korean forces have been training together for years, and routinely rehearse everything from beach landings to an invasion from the North, or even "decapitation" strikes targeting the North Korean regime.

Last month, the then nominee to head US and UN forces in South Korea said the pause in drills had been a "prudent risk" to help facilitate a detente on the peninsula.

But there "was certainly a degradation in the readiness of the force, for the combined forces," General Robert Abrams told the Senate Armed Services Committee at his confirmation hearing.

Abrams went on to say that the continued suspension of the drills risked a further erosion in "readiness and capability and interoperability of the combined forces," though he noted officials were working to minimize issues by running smaller scale staff exercises.