In this handout image provided by South Korean Defense Ministry, U.S. Air Force B-1B bomber (L), South Korea and U.S. fighter jets fly over the Korean Peninsula during the Vigilant air combat exercise (ACE) on December 6, 2017 in Korean Peninsula, South Korea.

The United States and South Korea have suspended upcoming joint air defense drills to give diplomatic efforts with North Korea "every opportunity to continue," the U.S. military said on Friday.

The Pentagon said the decision to suspend Exercise Vigilant Ace, which had been scheduled for December, was taken by U.S. Defense Secretary Jim Mattis and South Korean Defense Minister Jeong Kyeong-doo, who met in Singapore on Friday.

Pentagon spokeswoman Dana White said in a statement that the decision had been taken to "give the diplomatic process every opportunity to continue."

"Both ministers are committed to modifying training exercises to ensure the readiness of our forces. They pledged to maintain close coordination and evaluate future exercises," White said.

She added that Mattis had spoken with his Japanese counterpart as well on the issue.

The two Koreas have held three summits this year. North Korean leader Kim Jong Un also held an unprecedented summit with U.S. President Donald Trump in Singapore in June, where the leaders promised to work toward denuclearization of the Korean peninsula.

Vigilant Ace is one of several exercises that have been suspended since the summit to encourage dialogue aimed at getting North Korea to give up its nuclear weapons.

Last year, Vigilant Ace had more than 230 aircraft, including six F-22 Raptor stealth fighters, and around 12,000 U.S. service members.

Trump caught many U.S. officials off guard earlier this year when he announced after his summit with Kim that the United States was suspending the summers joint military drills with South Korea, known as Ulchi Freedom Guardian.

"If we continue to suspend the major exercises, our military capacity will begin to atrophy," said Abraham Denmark, a former deputy assistant secretary of defense for East Asia under President Barack Obama.

Denmark said the U.S. military could likely tolerate the suspension of major exercises for about a year before serious challenges to military readiness and capability.

Last month, the Pentagon's pick to be the new commander of U.S. forces in South Korea said the decision to suspend some joint exercises between South Korea and the United States was a "prudent risk" but had caused a "slight degradation" in military readiness.

Denmark said joint exercises were particularly important as a new commander, U.S. Army General Robert Abrams, takes charge of U.S. forces in South Korea.

Washington and Seoul both publicly insist they are on the same page about dealing with Pyongyang. But behind the scenes, there are growing signs of disagreement as South and North Korea forge ahead with plans to defuse military tensions and rebuild economic ties.

"The U.S. continues to make these major, substantive concessions and the North Koreans continue to drag out any sort of diplomatic process towards denuclearization," Denmark said.