North Korea fired some 500 artillery shells near the Northern Limit Line on Monday, with about 100 of them falling south of the de facto inter-Korean sea border.

The North began its live-fire drills at around 12:15 p.m., some four hours after notifying the South through a fax message that it had zoned off seven areas just north of the NLL for the drills.

In response to the 100 shells having dropped into its territorial waters, the South fired back some 300 shots with its K-9 self-propelled howitzers. All of the rounds fell north of the maritime border, Seoul’s Defense Ministry said.

The ministry called the North’s live-fire drills a “premeditated, deliberate” provocation.

“The live-fire drills came on the heels of the North’s launches of rockets and ballistic missiles, as well as the threat of another nuclear test. It is part of this provocative package,” ministry spokesperson Kim Min-seok told reporters.

“Given that the North fired the shots southward, we judge the drills to be a deliberate provocation. Those rounds having fallen in our waters were all concentrated in sensitive areas adjacent to Bangnyeongdo, meaning it was a very deliberate, threatening move.”

Amid the drills, the U.N. Command Military Armistice Commission sent a message to the North, calling on it to immediately halt the drills and end any hostile activities against the South. It also proposed a general-level meeting with the North.

Seoul officials said that the drills appeared intended to protest the ongoing South Korea-U.S. Foal Eagle military exercise and make waters south of the NLL a disputed zone. Pyongyang does not recognize the NLL as it was drawn unilaterally by the then U.S.-led UNC right after the end of the 1950-53 Korean War.

As the North pressed ahead with the drills, the South put its military on alert and mobilized its F-15K fighter jets to keep closer tabs on the North Korean military.

It also directed residents of the border islands, including Yeonpyeongdo and Bangnyeongdo, to be evacuated to safe locations and restricted the operations of fishing boats and passenger ships to and from the islands.

For Monday’s drills, the North mobilized a large number of coastal artillery pieces and multiple rocket launchers, including those mounted on warships.

Along its frontline coastal areas, the North has deployed some 1,000 artillery pieces with ranges of between 12 km and 27 km, and Samlet and Silkworm surface-to-ship missiles with ranges of between 83 km and 95 kilometers

The North’s artillery barrage came just as South Korean and U.S. marines kicked off “Ssangyong,” a joint eight-day amphibious landing exercise in the southeastern port city of Pohang.

Just a day earlier, the North threatened to conduct a “new type” of nuclear test in protest of the U.N. Security Council’s condemnation of its launch of two ballistic missiles last week.

South Korea’s political parties upbraided the North for firing artillery at South Korean waters, calling on the North to stop its provocations.

“We strongly condemn the provocation that all of a sudden damaged our utmost efforts to improve inter-Korean relations and promote mutual development,” said Saenuri Party spokesperson Min Hyun-joo.

“The North’s reckless provocations threaten the peace not only on the Korean Peninsula, but in Northeast Asia as a whole.”

The main opposition New Politics Alliance for Democracy also denounced the North for raising military tensions.

“We will not tolerate any North Korean moves that escalate tensions and could lead to a clash,” said its spokesperson Park Kwang-on. “Our government should deal sternly with military provocations while adhering to its principle of maintaining peninsular peace.”

Also on Monday, the North escalated its criticism of Seoul for having seized a fishing boat with three sailors on board. The South captured the vessel after it drifted across the NLL last Thursday, and returned it to the North hours later as no one onboard was willing to defect to the South.

Pyongyang argues that Seoul kidnapped the sailors and assaulted them in the process of the seizure. Seoul countered the argument, saying that Pyongyang warped the facts and violated a mutual agreement to stop slandering one another.

By Song Sang-ho (sshluck@heraldcorp.com)