Seoul, South Korea (CNN) — North Korea on Thursday showed off its long-range artillery systems, thousands of weapons that it could use to strike the South with little warning while causing tens of thousands of casualties, according to experts.

The North’s artillery drills come at a time of heightened tension on the Korean Peninsula as the United States and South Korea conduct their annual Freedom Shield exercise, which the South Korean military said will focus on deterring North Korea’s nuclear threats.

North Korea’s Defence Ministry on Monday denounced the 11-day US-South Korea joint exercises as “provocative” and “reckless,” and warned North Korean forces will monitor “adventurist acts” and conduct “responsible military activities” to bring what it called an unstable security situation under control, according to the state-run Korean Central News Agency (KCNA).

Thursday’s artillery exercise was the North’s second drill this week, a day after its ground forces appeared to infiltrate border guard posts during manoeuvres.

North Korean leader Kim Jong Un observed both drills and was seen in photos provided by state media.

***_{Kim Jong Un inspects the artillery firing drill of the Korean People’s Army (KPA) large combined units on March 7. (KCNA via CNN Newsource)}***

A KCNA report on Friday said the artillery drill sent a message to the South.

“The drill started with the power demonstration firing of the long-range artillery sub-units near the border who have put the enemy’s capital in their striking range and fulfilled important military missions for war deterrence,” the KCNA report said.

Kim stressed the importance of preparing “for regular combat mobilisation so that all the artillery sub-units can take the initiative with merciless and rapid strikes at the moment of their entry into an actual war,” the report said.

Ever-present threat

North Korea’s artillery systems have been making headlines in recent weeks as Pyongyang is arming Russian forces with them for combat in Ukraine.

Since August, Pyongyang has shipped about 6,700 containers to Russia, which could accommodate more than 3 million rounds of artillery shells or more than 500,000 rounds for multiple rocket launchers, according to the South Korean Defence Ministry.

While those weapons present a big challenge for Ukraine’s defenders, they are also an ever-present looming threat for South Korea and the US military forces stationed on the Korean Peninsula.

Artillery strikes are almost impossible to defend against, experts say.

***_{Multiple rocket launchers fire during a drill of the Korean People’s Army on March 7. (KCNA via CNN Newsource)}***

A 2020 report from the RAND Corp. Thinks Tank said North Korea’s artillery systems, with nearly 6,000 big guns within range of major South Korean population centres, present as great a danger to the South as Kim’s nuclear weapons and missile programs.

“If fired at civilian targets, those nearly 6,000 systems could potentially kill more than 10,000 people in only an hour,” the RAND report said.

In one scenario, a one-minute barrage on a 2.4-square-kilometre area of the capital Seoul using just 54 multiple rocket launchers, predicted more than 10,000 casualties.

“Because (North Korean) shelling could kill many thousands in just an hour, with little warning, it would be difficult for the Republic of Korea (ROK) and the United States, once the bombardment had begun, to halt it, or otherwise protect the ROK population, before it could do very serious harm,” the report said.

Even retaliatory strikes by South Korea and the US would be difficult to execute, the report said.

“Much of the DPRK’s artillery is located in heavily fortified hardened artillery sites (HARTS) with air defense capabilities deployed to their rear. These physical protective measures make air strikes and counter-battery fire against the DPRK artillery a challenge for U.S. and ROK forces,” the report said.

Kim has drawn an increasingly harder line against South Korea in recent months, saying the North will no longer seek reconciliation and reunification with the South and instructing the country’s army, munitions industry, nuclear weapons and civil defence sectors to accelerate war preparations in response to “confrontation moves” by the US.

In January, Kim called the South the North’s “primary foe and invariable principal enemy” and ordered a reunification monument in the North Korean capital to be demolished.