The U.S. will kick off its annual joint military exercises with South Korea on Monday, but this year’s drills will involve far fewer American troops than last year’s amid heated tensions with nuclear-armed North Korea.

The Pentagon said Friday that the exercises, known as Ulchi Freedom Guardian (UFG), would see about 17,500 U.S. service members take part in the drills scheduled to begin Monday and run through Aug. 31.

About 25,000 were involved in the 2016 drills.

South Korea’s Defense Ministry said about 50,000 South Korean forces will join the drills.

In a statement, the Pentagon did not address the discrepancy in the numbers, but the UFG exercises come amid soaring tensions over the North’s nuclear weapons ambitions. Pyongyang routinely blasts the drills as a rehearsal for invasion and warned last week of a “second Korean War” should Seoul and Washington go ahead with them.

The U.S., however, disputes this claim, saying the exercises are defensive in nature.

“UFG is computer simulated defensive exercise designed to enhance readiness, protect the region and maintain stability on the Korean peninsula,” the Pentagon said, adding that they “help to ensure peace and security on the peninsula, and reaffirm U.S. commitment to the Alliance.”

The exercises will be the first large-scale drills since North Korea conducted two successful tests of intercontinental ballistic missiles and later unveiled a plan to lob missiles near the U.S. territory of Guam. The North later walked back that threat, saying that it would instead keep an eye on the situation.

Beyond the smaller number of U.S. troops, the U.S. may chose not to involve any of its strategic assets in the drills.

South Korea’s SBS television network reported Friday that Washington had canceled plans to deploy two aircraft carriers, a nuclear-powered submarine and strategic bombers to the peninsula for the drills. Citing an anonymous South Korean government source, the report said Seoul had agreed with the proposal to scale back the exercises.

The U.S. has used its B-1B heavy bombers on Guam to showcase its ability to project “overwhelming force” over the Korean Peninsula. It last conducted such a mission over South Korea on Aug. 8, when two B-1Bs were joined by South Korean F-15 fighters.

North Korea labeled the U.S. as the “air pirates of Guam” and called the training exercise a “mad-cap drill simulating an actual war.”

But since Pyongyang unveiled its plan to fire missiles near Guam on Aug. 9, the U.S. has apparently refrained from sending strategic assets — including the Guam-based bombers — near the Peninsula.

Instead, the U.S. Air Force sent two B-1Bs from Andersen Air Force Base on Guam to link up with Air Self-Defense Force F-15s near the Senkaku Islands in the East China Sea on Wednesday.