Marines of the U.S., left, and South Korea, wearing blue headbands on their helmets, take positions after landing on a beach during the joint military combined amphibious exercise, called Ssangyong, part of the Key Resolve and Foal Eagle military exercises, in Pohang, South Korea, March 12, 2016. South Korea and the U.S. say they've decided to end their springtime military drills to back diplomacy with North Korea. Credit: Kim Jun-bum | Yonhap via AP

U.S. and South Korean officials announced Saturday that they will end longtime military exercises that had riled North Korean leader Kim Jong Un’s regime and drawn criticism from President Donald Trump, replacing them with smaller operations.

The Pentagon disclosed the decision Saturday evening after a phone call between acting defense secretary Patrick Shanahan and his South Korean counterpart, Defense Minister Jeong Kyeong-doo. They agreed “to conclude” the exercises, replacing them with “newly designed Command Post exercises and revised field training program,” according to a Pentagon statement.

“The Minister and Secretary made clear that the Alliance decision to adapt our training program reflected our desire to reduce tension and support our diplomatic efforts to achieve complete denuclearization of the Korean Peninsula in a final, fully verified manner,” the statement said.

A U.S. military official, speaking on the condition of anonymity because of the sensitivity of the issue, said the newer, scaled-back operation will be held March 4-12 and will entail a computer exercise. It will be called “Dong Maeng,” which means “Alliance,” the official said, and will include thousands fewer troops.

Another U.S. defense official, also speaking on the condition of anonymity because of the sensitivity of the discussions, said Shanahan had hoped to find a solution that would allow the U.S. and South Korean militaries to continue the parts of the exercises that focused on maintaining joint readiness while foregoing parts that in the past had been intended as a show of force.

Those elements, the Pentagon leadership has concluded, could be viewed as saber-rattling at a time when the military looks to support diplomacy with North Korea, the official said. The plans to scale back the exercise could have some impact on readiness, officials said, but it’s not yet clear how much.

Both the Foal Eagle series of exercises held in the spring and the Key Resolve exercises traditionally held in the summer will conclude. They focused on preparing for the possibility of war with North Korea, and involved thousands of troops. At times, they included U.S. bombers, submarines and other displays of force.

The announcement, which NBC News first reported Friday was expected, comes two days after Trump cut short a summit with Kim on Thursday after they were unable to agree to terms on how to denuclearize the Korean Peninsula. As he had previously, the president spoke warmly of Kim and with disdain for the exercises.

“I was telling the generals — I said: Look, you know, exercising is fun and it’s nice and they play the war games,” Trump said, referring to the exercises by a phrase the Pentagon has typically avoided. “And I’m not saying it’s not necessary, because at some levels it is, but at other levels it’s not. But it’s a very, very expensive thing. And you know, we do have to think about that, too.”

The president announced in June 2018 following his historic first summit with Kim that he would end all “war games” on the peninsula. The Pentagon said a few days later that it would suspend the Ulchi-Freedom Guardian exercise that was planned for August 2018 but avoided forecasting plans beyond that.

But as discussions continued, it became clear that future exercises also would be affected. Jim Mattis, who resigned as Pentagon chief in December, said in November that this spring’s Foal Eagle exercise would be “reduced in scope” as diplomats from the two countries continued to speak.

“Foal Eagle is being reorganized a bit to keep it at a level that will not be harmful to diplomacy,” he said.

Officials from the two Koreas have agreed on other measures to reduce tensions, including setting up buffer zones in waters around the peninsula and destroying some guard towers at the heavily fortified Demilitarized Zone that separates the countries.

Some Democrats have questioned whether the cessation of exercises will hurt the ability of the U.S. military to respond in the event of a crisis. Army Gen. Robert Abrams, the top commander of U.S. Forces Korea, downplayed the significance of scaled-back exercises last month.

Abrams, speaking before the Senate Armed Services Committee on Feb. 12, said that while some exercises have been canceled, the Americans and South Koreans continue to train together and have done “some innovative things” to stay sharp “by adjusting size, scope, volume and the timing” of their operations to allow diplomats to continue discussing peace.

“Historically we’ve conducted one in the spring and one in the summer, and I have continued planning for execution of one in the spring,” he said.

Under questioning, Abrams said that most rank-and-file U.S. troops would notice a difference in their training level, and that battalion commanders “might in the upcoming months.” Senior commanders would see a difference, he said, adding that they are well-versed in the demands of their job.

Washington Post writer Missy Ryan contributed to this report.