Meanwhile, the Pyongyang state media said that the incident happened as North Korean soldiers worked to permanently seal the frontier dividing the peninsula, according to a statement by Lt Gen Ko Jong Chol.

Ko called the event a “premeditated and deliberate provocation,” saying that Seoul’s military used a machine gun to fire more than 10 warning shots.

“This is a very serious prelude that would inevitably drive the situation in the southern border area, where a huge number of forces are stationing in confrontation with each other, to the uncontrollable phase,” said Ko.

The last time the two countries had an incident at the border was in early April, when South Korea fired warning shots at 10 North Korean soldiers, who briefly crossed the zone.

The North Korean military announced last October that it was planning to totally shut off the southern border, saying that it had sent a message to the US to “prevent any misjudgment and accidental conflict.”

Soon after, sections of unused yet deeply symbiotic roads and railroad tracts connecting the North to the South were blown up. Ko warned that North Korea’s army would retaliate against any interference in its plants to permanently seal the border.

Before Lee took office, relations between the two Koreas had reached the lowest point in years, but following his election, he promised to pursue dialogue with the mysterious nation, saying last week that the government “will take consistent measures to substantially reduce tensions and restore trust.”

Still, South Korea and the US began their annual joint exercises on Monday in preparation for potential threats from the North. Lee called the drills “defensive” and said they were “not intended to heighten tensions.”

But North Korea, which attacked the South in 1950, sparking the Korean War, has historically been insulted by these exercises, calling them rehearsals for invasion.

Earlier this week, North Korean Supreme Leader Kim Jong Un called for the “rapid expansion” of the country’s nuclear weapons capability, pointing it towards the ongoing US-South Korean military exercises, which he claimed could “ignite a war.”

His sister, Kim Yo Jong, the Deputy Director of the Publicity and Information Department, has said that Seoul “cannot be a diplomatic partner” of the North, calling President Lee “not the sort of man who will change the course of history.”