North Korea fired at least one unidentified projectile in an eastward direction Saturday, the Joint Chiefs of Staff (JCS) said, as South Korea and the United States were conducting their key springtime military exercise.

The JCS said it detected the launch, without providing further details.

The latest launch came as South Korea and the United States kicked off their annual Freedom Shield exercise Monday for an 11-day run.

The North has long denounced the allies' combined military drills as a rehearsal for an invasion, though Seoul and Washington have said the exercises are purely defensive.

Earlier this week, Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, condemned the ongoing military drills and warned of "unimaginably terrible consequences."

The North also recently test-fired strategic cruise missiles from the Choe Hyon destroyer, with the North Korean leader underscoring the need to maintain and expand a "powerful and reliable nuclear war deterrent," according to Pyongyang's state media.

North Korea last fired multiple short-range ballistic missiles toward the East Sea on Jan. 27, which it said was aimed at testing a renewed large-caliber multiple rocket launcher system. (Yonhap)