South Korean and U.S. special warfare units are holding a joint drill named the Teak Knife, according to Seoul's Joint Chiefs of Staff.

The exercise which kicked off early this month and is set to last through early March is under way at Camp Humphreys in Pyeongtaek and Osan Air Base.

Teak Knife is held for special forces to train infiltrating enemy camps. It also involves close air support, air control and hostage rescue missions.

Reportedly mobilized in the latest drill is the U.S. Air Force's AC-130J Ghostrider gunship which provides close-air support to troops fighting on the ground.

The allies have conducted the Teak Knife annually since the 1990s but kept it undisclosed due to the sensitive nature of the operation.

Last year the USFK's Special Operations Command Korea (SOCKOR) revealed the drills via social media through a series of photos showing key activities of the Exercise Teak Knife.  

This year, the event is expected to be made public, seen as a warning to North Korea and its continued provocations.