Seoul defense officials say South Korean troops have fired warning shots after North Korean soldiers approached too close to the border separating the rival countries.

The officials say Monday's incident happened near the military demarcation line inside the 4-kilometer-wide (2.5-mile-wide) Demilitarized Zone that divides the Korean Peninsula.

They say North Korean soldiers retreated after South Korean troops fired 20 rounds of warning shots. There were no reports of casualties.

The officials spoke on condition of anonymity in line with office policy.

Tensions between the Koreas remain high after troops exchanged gunfire along the border twice last month, though there have been no reports of casualties.

The Korean Peninsula remains in a technical state of war because the Korean War in the 1950s ended with an armistice, not a peace treaty.