The Defense Ministry issued a statement Monday and warned that if North Korea fires shells south of the Northern Limit Line border, Seoul will "mercilessly" respond.

The Joint Chiefs of Staff earlier said the North fired about one hundred artillery shells into the East Sea on Monday from a site near the military demarcation line in Goseong, Gangwon Province.

The JCS said the North fired northeast from 11:43 a.m. to 12:15 p.m. from a site some hundreds of meters north of the Northern Limit Line (NLL). It said the shells fell one to eight kilometers north of the NLL in the East Sea but none of them fell south of the border.

With the shells falling close to the NLL, columns of water were observed from the Unification Observatory in Goseong.

The launch location is believed to be an artillery base behind Mount Geumgang's Guseon Peak.

It's unusual for the North Korean army to hold artillery drills immediately north of the East Sea military demarcation line.

According to North Korean media reports, Kim Jong-un appears to have commanded the drill.

Considering Pyongyang's recent moves including the test launch of short-range ballistic missiles, the Monday fire is viewed as the North's military protest to the South.

The North’s military moves are in contrast with its decision to take part in the Incheon Asian Games to which it had also planned to send a cheering squad.

The North has also more than once issued statements calling for improvements in inter-Korean relations.

The unannounced shootings are therefore regarded a show of force in protest to the Ulchi Freedom Guardian South Korea-U.S. joint exercise scheduled in mid- to late August and also resistance to a U.S. aircraft carrier that made port call in Busan on July 11.

But most pundits say it’s more likely the regime is simply trying to highlight its presence than really trying to worsen the situation on the Korean Peninsula.