The last time the two sides exchanged fire on the border was in 2014, with North Korean soldiers also shooting at a defector in 2017 but the South did not fire back.
A fresh mark on Kim Jong-un's arm corroborates earlier reports about his alleged heart surgery, some medical experts suggested after footage of the North Korean leader's most recent public outing was published by local media.
U.S. President Donald Trump on Saturday welcomed the reemergence of North Korea's Kim Jong Un after weeks of speculation about his health, but prospects for the U.S. efforts to persuade Pyongyang to denuclearize appear as bleak as ever. It added that it was communicating with North Korea through a military line while staying prepared for further fire.
Ms Choi said North Korea had yet to respond.
Under the accord, the two Koreas set up land, maritime and ground buffer zones and agreed to halt all hostile acts against each other, aimed at reducing tensions and building trust.
Background: The DMZ is in reality the most militarized border in the world, acting as a a 155-mile-long buffer zone between the two countries with mines, guard posts and almost two million troops on both sides.
North Korean state media released this image they say is of leader Kim Jong-un at the fertiliser plant
The South Korea government, which had urged caution on speculation about Kim's health and said it saw no sign anything serious had happened, gathers intelligence from various sources including US spy agencies and satellite imagery, said Kim Hong-kyun, a former South Korean nuclear envoy.
Speculation about Mr. Kim's health has been rife after he missed the birthday celebrations of late state founder Kim Il Sung on April 15.
Despite Kim's prolonged disappearance from public view since he was last seen on April 11 presiding over a major party meeting, North Korean media outlets continued to carry articles on his routine schedules, such as sending out letters to foreign leaders or gifts to honored citizens and workers, though they provided no report or photo on his public activity.
"Our assessment is that (Kim) did not undergo surgery", a South Korean official told reporters. Trump wrote in a Saturday tweet.
USA president Donald Trump said Saturday he was "glad" about Kim's reappearance and about the fact that he is apparently healthy.
The North Korean leader expressed gratitude to state propagandists, Yonhap News Agency cited the North Korean media.
Coronavirus: First California county reopens in 'new normal'
For example, the city of San Diego allows its citizens to walk, jog and swim on the coast but prohibits stopping and sitting. Needless to say, numerous protesters were unmasked and almost all were practicing the opposite of physical distancing.