South Korea has confirmed it fired warning shots earlier in the week at North Korean soldiers who briefly crossed the heavily-fortified border between the two countries.
North Korean state media called the shots a "deliberate provocation" and Pyongyang has accused Seoul of risking "uncontrollable" tensions.
The incident was made public as new South Korean President Lee Jae Myung departed Seoul on Saturday for a visit to Tokyo and Washington.
Pyongyang has upped the ante in recent weeks, with leader Kim Jong Un's sister rebuffing efforts towards reconciliation made by Lee's government.
The incident took place amid continuing work by North Korea since last year to permanently seal its border with the South.
