The U.S. and South Korea have decided to cancel another joint military exercise on the peninsula amid negotiations on the North’s nuclear program, the Pentagon said on Friday.

The decision to suspend the Vigilant Ace exercise held in December comes after a meeting between Defense Secretary Jim Mattis and South Korean Minister of Defense Jeong Kyeong-doo this week.

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The two leaders wanted “to give the diplomatic process every opportunity to continue,” chief Pentagon spokeswoman Dana White said in a statement.

“Both ministers are committed to modifying training exercises to ensure the readiness of our forces,” White said.

The Pentagon previously canceled the Ulchi Freedom Guardian exercise with South Korea over the summer after President Trump called the "war games" expensive and unnecessary following a June summit in Singapore with dictator Kim Jong Un over giving up the North's nuclear arsenal.

At a news conference in August, Mattis made clear that while the U.S. was canceling major named exercises as a matter of “good faith,” routine readiness training for U.S. and South Korea forces would continue.

“Remember that what we did when we suspended the exercise, ladies and gentlemen, we suspended several of the largest exercises but we did not suspend the rest,” Mattis said. “So there are ongoing exercises all the time on the peninsula.”

The secretary has also said the effects of canceling the exercises is "negligible." However, the new U.S. commander in South Korea, Gen. Abe Abrams, told the Senate during his September confirmation hearing that the earlier cancellation caused a "slight degradation" in military readiness.

"If the impact of these exercises was negligible then you would have to ask the question why would you even be doing them. So obviously there is a value in interoperability with our allies and military readiness in general," said Tom Spoehr, the director of the Center for National Defense at the Heritage Foundation. “I think what people have done is look at the value versus what we might gain out of a successful negotiation with North Korea and say, hey, this risk is worth it in the bigger picture."

Secretary of State Mike Pompeo has been working for months to negotiate a deal with the North to abandon its nuclear program, which includes warheads and tested intercontinental ballistic missiles that might be capable of striking American cities.

Meanwhile, the Vigilant Ace exercise has been running for a decade to prepare the U.S. and South Korea for an air and ground war with the North. Last year, it involved 230 military aircraft including F-35 joint strike fighters and F-22 Raptors.

Spoehr said he expects more joint exercises could be canceled in the future and for now the U.S. military must depend on smaller scale exercises with its South Korean counterparts to remain prepared for a conflict.

The next large exercise in Korea could be Foal Eagle, which involves tens of thousands of U.S. personnel. Trump and South Korean President Moon Jae-in agreed last year to delay the exercise's February start date amid the Olympics and a diplomatic thaw with the North.

Another cancellation could put increased emphasis on the smaller scale interactions between American troops and their South Korean counterparts, said Michael O’Hanlon, a senior fellow at the Brookings Institution.

As Mattis has said, the military continues to work with the Koreans at the brigade and squadron level despite the suspension of Ulchi Freedom Guardian and Vigilant Ace. The smaller interactions continue largely out of the public eye and have not drawn the ire of the North.

"My view is actually that the really big exercises are never needed, if and only if, we can replace them with a sufficient number of demanding smaller ones," O'Hanlon wrote in an email.