South Korea has asked North Korea for an explanation after an exchange of fire on the heavily fortified border was reported on Sunday.
Military officials in South Korea said it returned fire after several bullets fired from North Korea hit one of its front-line guard posts, in the first shooting inside the Demilitarized Zone in more than two years.
No casualties have been reported one either side.
Defense Ministry spokeswoman Choi Hyun-soo told reporters on Monday that South Korea sent a message of strong protest and urged North Korea to explain the shooting and avoid similar incidents. Choi said North Korea hasn’t responded to the message.
The 248-kilometer Demilitarized Zone bisects the Korean Peninsula and is guarded by mines, barbed wire fences and combat troops on both sides. It was formed as a buffer after the end of the Korean War and officially is jointly overseen by North Korea and the American-led UN Command.
The shooting came a day after North Korea broadcast images of leader Kim Jong Un reappearing in public after a 20-day absence amid intense speculation about his health.
Kim earlier vanished from the public eye after presiding over a Politburo meeting of the ruling Workers' Party on April 11 to discuss the coronavirus.
Speculation about his health began swirling after he missed an April 15 event commemorating the birthday of his grandfather and state founder, Kim Il Sung, something he had never done since inheriting power upon his father Kim Jong Il's death in late 2011.
In late 2018, the two Koreas began destroying some of their front-line guard posts and removing mines from the DMZ as part of steps to reduce tensions.
But the efforts stalled amid a deadlock in nuclear negotiations between Kim and President Donald Trump meant to convince North Korea to give up its arsenal in exchange for lifting economic sanctions.
The last time there was gunfire along the border was in 2017, when North Korea sprayed bullets at a soldier fleeing to South Korea.