PYONGYANG, North Korea — North Korean leader Kim Jong Un on Friday declared his frontline troops in a “quasi-state of war” and ordered them to prepare for battle a day after the most serious confrontation between the rivals in years.

South Korea’s military on Thursday fired dozens of artillery rounds across the border in response to what Seoul said were North Korean artillery strikes meant to back up a threat to attack loudspeakers broadcasting anti-Pyongyang propaganda.

The North’s declaration Friday is similar to its other warlike rhetoric in recent years, including repeated threats to reduce Seoul to a “sea of fire,” and the huge numbers of soldiers and military equipment already stationed along the border mean the area is always essentially in a “quasi-state of war.” Still, the North’s apparent willingness to test Seoul with military strikes and its recent warning of further action raise worries because South Korea has vowed to hit back with overwhelming strength should North Korea attack again.

Pyongyang says it did not fire anything at the South, a claim Seoul dismissed as nonsense.

Kim Jong Un ordered his troops to “enter a wartime state” and be fully ready for any military operations starting Friday evening, according to a report in Pyongyang’s official Korean Central News Agency. The North has also given Seoul a deadline of Saturday evening to remove border loudspeakers that, after a lull of 11 years, have started broadcasting anti-Pyongyang propaganda. Failure, Pyongyang says, will result in further military action. Seoul has vowed to continue the broadcasts.

The North’s media report said that “military commanders were urgently dispatched for operations to attack South Korean psychological warfare facilities if the South doesn’t stop operating them.”