North Korean leader Kim Jong-un was reported on Thursday to have directed live-ammunition drills targeting South Korea’s frontline islands, further escalating tension around the Northern Limit Line, a de facto maritime border.

Following a recent series of military inspections, Kim oversaw the drills on Wednesday apparently in protest against the ongoing South Korea-U.S. Key Resolve exercise, which the North denounced as a “rehearsal for a nuclear incursion.”

“Leader Kim Jong-un directed live-ammo drills to gauge the actual combat capabilities of the artillery units located at flashpoints near Yeonpyeongdo and Bangnyeongdo,” said the North’s official Korean Central Television.

“This exercise has the objective to confirm the possibility of our firepower and strike capability, check our weapons systems and construct our measures (to respond to a contingency).”

It was the first time that Pyongyang’s mouthpiece had specifically referred to South Korea’s frontline islands as targets for a military exercise.

The North’s top military officers such as Choe Ryong-hae, the director of the General Political Bureau, General Staff Chief Hyon Yong-chol and Kim Kyok-sik, the minister of the People’s Armed Forces, accompanied Kim during the drills.

To help assuage security concerns, South Korea’s Prime Minister Chung Hong-won flew to Yeonpyeongdo and inspected evacuation facilities. He urged people to focus on their daily lives, stressing the government was fully ready to counter any North Korean provocations.

Following the North’s artillery shelling of the island in November 2010, the government built 42 evacuation facilities on the border islands, including seven on Yeonpyeongdo and 26 on Bangnyeongdo, with a budget of 53 billion won ($47 million).

During Kim’s inspection of an artillery unit late last month and his visits to two frontline islands earlier last week, he referred to the artillery attack on Yeonpyeongdo as a “thrilling win.”

Amid a series of reports on Kim’s military inspections, concerns have been raised that the North could make provocations or saber-rattling moves near the NLL, which it has long sought to nullify. Pyongyang argues that the maritime border is invalid as it was drawn unilaterally by the U.S.-led U.N. Command at the end of the 1950-53 Korean War.

Meanwhile, the Rodong Sinmun, the daily of the North’s ruling Workers’ Party, criticized conservatives here in the South calling for nuclear armament.

“It goes without saying that (South Korean) puppets crazy about a nuclear war of incursion would bring about a horrendous nuclear catastrophe on the head of our nation as a whole, if they were armed with nuclear weapons,” it said in a piece.

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