South Korea's military has staged joint defense drills for western border islands to bolster readiness against North Korean threats, the Marine Corps said Friday.

The three-day exercise began Wednesday on the border islands in the Yellow Sea, including Baengnyeong Island, joined by troops from the Army, the Navy, the Air Force and the Marine Corps.

The Marine Corps said the annual joint drills are "defensive" in nature to enhance the military's joint capabilities.

The maneuver mobilized UH-60 and CH-47 helicopters, F-15K and KF-16 fighter jets, destroyers, frigates, landing ships and amphibious assault ships to stage artillery firing, counterterrorism operations and maritime live exercises, among others.

Tensions near the front-line islands escalated after North Korea in January fired hundreds of artillery shells from its west coast into the maritime buffer zone near the Northern Limit Line, the de facto inter-Korean maritime border in the Yellow Sea.

In January, North Korean leader Kim Jong-un threatened South Korea with war if "even 0.001 mm" of the North's territory is violated, saying his country will not recognize the NLL. (Yonhap)