South Korea fired artillery rounds toward North Korea after the North launched a shell toward a South Korean loudspeaker that had been blaring anti-Pyongyang broadcasts. (Reuters)

Tensions on the Korean Peninsula heightened Friday morning, when North Korean leader Kim Jong Un ordered his military chiefs to the border with South Korea and told them to put front-line troops in “a war-time state.”

Pyongyang has given Seoul a deadline of 5 p.m. Saturday, local time, to dismantle speakers blaring anti-North messages across the border or face “strong military action.”

Although analysts warned that this was likely just sabre rattling from Kim’s regime, the pronouncements, coupled with rare artillery fire across the 2.5-mile-wide demilitarized zone that separates the two Koreas, is causing jitters.

“The possibility of miscalculation and inadvertent escalation is much higher than it was a few days ago,” said Daniel Pinkston, Korea expert at the International Crisis Group.

Kim, the 30-something North Korean leader, called an emergency meeting of the powerful Central Military Commission Thursday night, the North’s Korean Central Television reported. This came a few hours after a rare exchange of artillery fire between the countries across the DMZ.

North Korea — angry that the South has resumed propaganda broadcasts across the border for the first time since 2004, retribution for a landmine attack that Seoul blames on Pyongyang — fired two rockets over the border toward the speakers Thursday afternoon. South Korea responded with several dozen 155 mm rounds.

Kim ordered military chiefs to the DMZ and told them to be ready for “surprise” military operations.

“Commanders of the Korean People’s Army were hastily dispatched to the front-line troops to command military operations to destroy psychological warfare tools if the enemy does not stop the propaganda broadcast within 48 hours and prepare against the enemy’s possible counteractions,” the television network reported, according to the South’s Yonhap News Agency.

The speakers have been delivering news of the outside world to information-starved North Koreans. Pyongyang responded by setting up its own speakers, broadcasting messages lauding the Kim regime and its communist system.

The war of words began last week after an attack that left two South Korean soldiers severely injured. They were patrolling on a known path in the DMZ when they stepped on a land mine, causing one soldier to lose both his legs while the other lost one. Seoul has blamed Pyongyang for deliberately planting the mines.

The escalation also coincides with annual military exercises in the South. More than 80,000, led by South Korea and the United States, are simulating the defense of South Korea in the face of an external attack. North Korea protests the drills, viewing them as preparations for an invasion.

In Seoul, the South Korean government raised its alert level and President Park Geun-hye canceled her meetings to focus on the threat.

South Korea “will strongly retaliate against any kind of North Korean attacks and the North will have to take all the responsibility for such retaliative actions,” a spokesman for the defense ministry said, quoting a message sent to the North earlier in the day.

China’s ambassador to South Korea, meanwhile, called on both Koreas to exercise restraint. “I hope they resolve their dispute through dialogue, not confrontation,” Qiu Guohong said during a breakfast function, Yonhap reported. “We oppose unilateral provocation from any side.”

In the United States, the Pentagon said it was “closely monitoring the situation” and was “concerned” by Thursday’s attack from the North.

“Such provocative actions heighten tensions, and we call on Pyongyang to refrain from actions and rhetoric that threaten regional peace and security,” said Capt. Jeff A. Davis, Defense Department spokesman. “The United States remains steadfast in its commitments to the defense and its allies, and will continue to coordinate closely with [South Korea].”

Pinkston of the International Crisis Group noted that it was significant that the pronouncements came through the Central Military Commission, rather than through the National Defense Commission, although Kim chairs both.

It is the NDC that has the authority to declare war and peace, and to mobilize the country for war. In wartime, civilian resources are allocated to the war effort through the NDC.

That led Pinkston to believe that the threats were part of a calculation.

“If they were planning on going to war, they would make an announcement through the NDC and mobilize reservists and the civilian economy for the war effort,” he said. “The CMC deals with military policies.”