The U.S. and South Korean air forces flew fighter jets in formation as part of a joint drill Tuesday, at a time when North Korea is expected to be imminently conducting a nuclear test explosion.

U.S. Deputy Secretary of State Wendy Sherman is currently on a trip to Seoul, where it is set to meet with South Korean and Japanese officials to discuss the growing threat posed by North Korea.

"Any nuclear test would be in complete violation of U.N. Security Council resolutions. There would be a swift and forceful response to such a test," Sherman said, after a meeting with South Korean Vice Foreign Minister Cho Hyun-dong. "We continue to urge Pyongyang to cease its destabilizing and provocative activities and choose the path of diplomacy,"

According to South Korea’s Joint Chiefs of Staff, Tuesday's exercise involved 16 South Korean planes that included F-35A stealth fighters, plus four U.S. F-16 fighter jets. A day earlier, the two countries fired eight surface-to-surface missiles into South Korean waters after North Korea fired eight missiles of their own from different spots on Sunday.

SOUTH KOREA, US LAUNCH EIGHT MISSILES IN RESPONSE TO NORTH KOREA MISSILE TESTS

U.S. and South Korea fighter jets in joint drill

In this photo provided by South Korea Defense Ministry, U.S. and South Korea Air Force fighter jets including South Korea's F-35A stealth fighters – and U.S. F-16 fighter jets, fly in formation during a joint drill on Tuesday, June, 7, 2022. (South Korea Defense Ministry)

The joint air drill comes after the U.S. and South Korea engaged in a joint navy exercise in international waters near Japan as part of a renewed effort to deter North Korea.

US, SOUTH KOREA CONDUCT JOINT NAVY DRILLS AHEAD OF POSSIBLE NORTH KOREA NUCLEAR TEST

The U.S. aircraft carrier Ronald Reagan led the three-day exercise, joined by Korean vessels, including the amphibious landing ship Marado and two destroyers. The U.S. also deployed a cruiser and replenishment tanker to bolster the fleet. 

Kim Jong Un

FILE - In this photo provided by the North Korean government, North Korean leader Kim Jong Un attends at a meeting of the Workers' Party of Korea in Pyongyang, North Korea on Feb. 28, 2022. (Korean Central News Agency/Korea News Service via AP)

North Korea has conducted six nuclear test detonations, the most recent being in September 2017. State Department spokesman Ned Price has said that the U.S. believes North Korea could look to conduct its seventh test "in the coming days."

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According to The Associated Press, the expected test could lead to North Korea claiming that they can build small bombs to be clustered on a multiwarhead intercontinental ballistic missile on short-range missiles that hit South Korea or Japan.

Fox News' Peter Aitken and The Associated Press contributed to this report.