South Korean Marines have conducted a massive exercise on defending a front-line island near the tense western sea border with North Korea, their command said Thursday.

The three-day drill took place on Baengnyeong Island, just south of the Northern Limit Line (NLL) in the Yellow Sea, involving "all troops and combat assets" of the 6th Marine Brigade, such as AH-1S Cobra attack choppers, Korea Amphibious Assault Vehicles and M48A3K battle tanks, the Marine Corps said.

"The training was held day and night from Tuesday through Thursday, led by the Northwest Islands Defense Command, focusing on reviewing the defense posture for the northwestern islands and preparedness for specific actions when necessary," it said.

South Korean Marines conduct a training on Baengnyeong Island in this photo provided by the Marine Corps. (Yonhap)

It cited the North's constant provocations and threats, highlighted by a series of missile and nuclear tests.

In late August, the North's special operation forces also staged a simulated attack on the South's border islands under the "field guidance" of leader Kim Jong-un, according to Pyongyang's state media.

South Korean Marines mobilize battle tanks in a drill on Baengnyeong Island in this photo provided by the Marine Corps. (Yonhap).

The Marine Corps said it's seen as suggesting the possibility of the North's "direct provocation," rather than a routine training.

The South's Marines also plan to hold a similar exercise on defending Yeonpyeong Island also close to the NLL, which serves as the de facto maritime border between the two Koreas still technically at war after their 1950-53 conflict ended in a truce.

An AH-1S Cobra attack helicopter fires rockets during a training held on Baengnyeong Island in this photo provided by the Marine Corps. (Yonhap)
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