South Korea and the US began joint air exercises on Monday, according to a Seoul military official, amid tensions over North Korea's recent missile tests and calls for denuclearization talks to resume.

Previously known as Vigilant Ace, the exercises once mobilized tens of thousands of troops, as well as hundreds of cutting-edge fighter jets, bombers, and other warplanes.

However, the program has been scaled back since 2017 to facilitate talks aimed at ending Pyongyang's nuclear and missile programs in exchange for sanctions relief from the United States.

The allies started the five-day drills without announcing or naming them. According to South Korea's Yonhap news agency, about 100 aircraft from each side were dispatched, including South Korean F-15Ks, KF-16s, and US F-16s, with no equipment or soldiers from the US mainland taking part in the exercises.

A spokesman for the South Korean Air Force declined to confirm the report, Yonhap news agency further reported.

North Korea fired at least one submarine-launched ballistic missile off its east coast, South Korea and Japan confirmed Tuesday, and the air drills came in response to that.

The US has lately called on North Korea to stop what it described as "destabilizing provocative activities."

On his part, North Korean leader Kim Jong-Un said that Pyongyang needs its arsenal to defend itself against a possible US invasion, adding that the US is the "root cause" of tensions in the Korean Peninsula.