He defected from a North Korean guard post nearby and was being treated in hospital.
"Currently, there are no unusual signs in the North Korean military, but we are increasing alertness against the possibility of North Korean provocations", officials told Yonhap News Agency.
The number of North Koreans defecting to South Korea in the first two-thirds of this year dropped by 13% compared with 2016.
We're Getting A Spider-Man Spinoff Movie All About Morbius
Sony Pictures is moving forward with a Morbius the Living Vampire movie as part of their Spider-Man spinoff universe. The project is said to be have been submitted to the studio "after a secret development process".
The soldier shot and injured by the North Korean side while defecting from a military post in front of Panmungak, the main building managed by North Korea in the Joint Security Area, the JCS said in a statement.
The majority of the defectors flee via China, which has the longest border with North Korea that is easier to cross than the heavily protected DMZ.
South Korean soldiers ride on an armored vehicle during a South Korea/United States combined training exercise at the U.S. Army's Rodriguez shooting range in Pocheon, northeast of Seoul, Sep.
South Korea and the United States were also conducting joint military drills in the East Sea utilizing three US aircraft carriers.
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Earlier on Monday, the Israeli military elevated the level of preparedness near the separation fence between Israel and Gaza. Israel said it is holding the bodies of five Palestinians killed in last month's tunnel attack in Gaza.
The drill comes in response to the series of nuclear and missile threats from North Korea and is created to show tyrannical leader Kim Jong-un that any further threats will be repelled with "overwhelming force". It has conducted a series of tests with the last being on September 3.
The drills occurred as President Donald Trump wrapped up a 12-day trip across Asia, in which the North Korean threat was at the top of his agenda.
Separately on Monday, a 58-year-old man from Louisiana was arrested Monday when he entered a controlled area in Yeoncheon County on the North Korea border.
Low mortgage rates not impressing potential new home buyers
One of the problems is that once rates reach rock bottom (which is pretty well where they are right now) the only way is up. This could be a good time for more young Americans to take out a Roth Individual Retirement Account or IRA for short.