Dozens of North Korean soldiers crossed the inter-Korean border in the heavily-fortified demilitarized zone(DMZ) dividing the two Koreas at around 8:30 a.m. Tuesday.

The North Korean soldiers returned to the northern side of the buffer zone immediately after the South Korean military fired warning shots.

The South Korean Joint Chiefs of Staff told reporters about the trespass by around 20 to 30 troops, which the military believes was accidental.

The DMZ is thick with bushes in the current season, making the military demarcation line(MDL) difficult to see.  

On June 9, dozens of North Korean soldiers crossed the MDL and returned to their side after the South Korean military fired warning shots. 

The North is currently constructing what appear to be antitank barricades and carrying out other works on the northern side of the DMZ.