In this file photo taken on April 02, 2017 South Korean Marines take position on a beach as amphibious assault vehicles fire smoke shells during a joint landing operation by the U.S. and South Korean Marines in the southeastern port of Pohang. AFP-Yonhap

South Korea and the United States are preparing to stage a joint military exercise this fall, the Pentagon said Tuesday, after North Korea warned the drill will affect the prospects of working-level nuclear talks between the two countries.

The North's foreign ministry issued the warning Tuesday, arguing that the "19-2 Dong Maeng" exercise, slated for around August, runs counter to the commitment that U.S. President Donald Trump made when he held a surprise meeting with North Korean leader Kim Jong-un on June 30.

"If the military exercise really goes ahead, it would affect the DPRK-U.S. working-level talks," the North said. "We will formulate our decision on the opening of the DPRK-U.S. working-level talks, while keeping watch over the U.S. move hereafter."

Asked about the U.S. stance, Pentagon spokesman Lt. Col. Dave Eastburn said the exercise program was already adjusted in cooperation with South Korea in order to maintain their readiness posture and to support diplomacy with North Korea.

The spokesman added that this regular exercise shows the U.S. commitment to the South Korea-U.S. alliance and to the defense of the Korean Peninsula.

Also Tuesday, Mark Esper, President Donald Trump's nominee for Secretary of Defense, said that the allies' joint exercises are "essential" to maintaining the readiness of the U.S. forces stationed in South Korea.

In a written answer submitted to the Senate Armed Services Committee ahead of his confirmation hearing, Esper also stressed that the allies' joint exercises ensure that the U.S. and South Korean militaries "can respond together to any potential North Korean military threat."

Speaking of a contingency on the peninsula, he vowed to eliminate the threat "without causing unintended effects on the broader North Korean population" in close cooperation with authorities concerned.

The answer is believed to have been written before North Korea issued the statement.

According to diplomatic sources earlier this week, Washington has proposed to the North holding a working-level meeting, but Pyongyang has yet to respond.

The nuclear negotiations have been stalled since the no-deal Hanoi summit between U.S. President Donald Trump and North Korean leader Kim Jong-un in February.

In his opening remarks at the hearing later in the day, the nominee stressed the need for military preparedness to respond to regional threats posed by North Korea, as well as Iran and terrorist groups.

"Our adversaries must see diplomacy as their best option, because war with the United States will force them to bear enormous costs," he said.

Seoul and Washington plan to hold the command post exercise around August in replacement of the summertime Ulchi Freedom Guardian as part of a reorganization of major exercises aimed at supporting peace efforts with the North.

Dong Maeng means alliance in English.

During the exercise, the two sides plan to test South Korea's initial operational capability (IOC) in an initial step to verify whether Seoul is on course to meet the conditions required for its envisioned retaking of wartime operational control of combined forces from Washington.

In March, the allies first launched the Dong Maeng exercise that replaced their springtime Key Resolve and Foal Eagle exercises.

North Korea has demanded that Seoul and Washington stop joint military exercises, calling them rehearsals for invasion. But the allies have said the drills are defensive in nature.

Issuing a brief release, South Korea's defense ministry also said, "Discussions are under way to stage a joint exercise with the U.S. later this year to verify (the ongoing process for) the transition of the wartime operational control of combined troops (from Washington to Seoul)."

Noting that the allies abolished the Freedom Guardian exercise, the ministry voiced hope for the swift resumption of the working-level dialogue. (Yonhap)