North Korean troops have repeatedly crossed into the demilitarized zone (DMZ) separating North Korea from South Korea this month.
On Tuesday morning, North Korean soldiers were observed working within the DMZ.
South Korean military officials released photographs of the North Korean soldiers, who were carrying tools, around 8:30 a.m. according to the Joint Chiefs of Staff.
South Korean forces fired warning shots to deter the North Koreans, who dispersed and returned to their territory.
It is estimated that 20 to 30 North Koreans entered the DMZ during the incident.
A similar incursion into the DMZ occurred earlier this month on June 9, when a large group of North Korean soldiers crossed into the forbidden area.
The June 9 incident prompted a similar response from South Korean guards, who broadcast warning messages and fired warning shots until the North Koreans left the area.
These interactions have increased tensions between the two Koreas just as North Korean leader Kim Jong Un is expected to host Russian President Vladimir Putin this week.
Putin is scheduled to visit Pyongyang for two days starting on Tuesday for his first official state visit to the communist nation in 24 years.
Russia has maintained North Korea as an ally despite Western sanctions imposed over the invasion of Ukraine.
In recent years, North Korea has served as a valuable intermediary for Russia by conducting business and manufacturing operations outside the scope of international law.