"North Korean has detonated parts of the Gyeongui and Donghae roads north of the Military Demarcation Line at around noon," the Joint Chiefs of Staff of South Korea reported, as quoted by the Yonhap agency.
The South Korean military has stepped up surveillance and readiness, the ministry said.
The North Korean Foreign Ministry said on Friday that South Korea had flown drones over Pyongyang three times since last week — on October 3, 9 and 10 — to distribute leaflets, calling the move a military provocation and a violation of its sovereignty.
Photos that North Korea presented as evidence showed what appeared to be a drone, presumably taken with thermal imaging equipment.
The South Korean military has denied the accusation of sending drones to North Korea, saying nothing of the sort happened.
The General Staff of the Korean People's Army on September 13 ordered border artillery units to be put on full alert for firing.
Earlier, it was reported that the General Staff of the North Korean Army said that North Korea would carry out work to block and cut off all roads and railways connecting its territory with the "main enemy" South Korea from October 9, and would fortify defensive structures, which it notified the American troops about in order to avoid clashes.