Coastal artillery bunkers in North Korea are seen from an observatory on Yeonpyeong Island, a South Korean border island in the West Sea, Jan. 7. Yonhap

Some of the artillery shells recently fired by the North Korean military fell just above the Northern Limit Line (NLL) in the Yellow Sea, a military source said Sunday, stoking tension on the tensely guarded western border, where past naval skirmishes have taken place.

North Korea fired some 200 artillery shells from its southwestern coastal areas Friday, prompting the South Korean troops on the front-line islands of Yeonpyeong and Baengnyeong to stage live-fire drills in response.

Most of the North Korean shells splashed into the maritime buffer zone, with some falling in waters as close as 7 kilometers north of the NLL, according to the source.

The latest saber-rattling came after Pyongyang in November vowed to restore military measures halted under a 2018 inter-Korean military agreement, which set up buffer zones in land, sea and air and banned live-fire drills near the border area to prevent accidental clashes.

"As North Korea vowed to scrap the inter-Korean military pact and conducted live-fire drills near the maritime buffer zone, mutually agreed buffer zones that ban hostile acts no longer exist," a military official said, asking for anonymity.

The South Korean military is considering taking corresponding measures when North Korea's artillery shells cross the NLL or land near the de facto maritime border, according to the official.

North Korea's Friday artillery firing marked the 16th one of its kind, including a missile launch in December 2022. The South Korean military conducted live-fire drills near the maritime buffer zone for the first time since the signing of the 2018 pact.

On Saturday, the North carried out live-fire drills for the second consecutive day to fire around 60 shells from the western coast, which landed in the maritime buffer zone above the NLL, the Joint Chiefs of Staff (JCS) said.

The South Korean military didn't conduct live-fire drills in response, considering them less threatening compared with Friday's exercise, military officials said.

On Sunday, Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, claimed the North conducted a "deceptive operation" by detonating explosives simulating the sound of 130 millimeters coastal artillery the previous day, according to the North's official Korean Central News Agency.

The vice department director of the ruling Workers' Party's Central Committee said the deceptive operation was aimed at exposing the South Korean military's detection capability, warning of "immediate actions" if the South provokes.

In response, the JCS called Kim's statement on the South Korean military's detection capability "psychological warfare," urging the North to cease acts that escalate tension in the border area.

Naval skirmishes between South and North Korea took place near the western maritime border in 1999, 2002 and 2009.

In 2010, North Korea fired a barrage of artillery shells on Yeonpyeong Island, killing two South Korean Marines and two civilians.

The North has contested the legitimacy of the NLL — drawn unilaterally by the U.S.-led U.N. Command after the 1950-53 Korean War — in recent decades and has demanded that it be redrawn, a request that the South has rejected. (Yonhap)