At a press briefing, ministry spokesman Kim Min-seok said the military has removed most of the mines buried near an air defense artillery unit on Mount Umyeon, but "about 10 mines" have not been recovered.
Dozens of homes in southern Seoul were buried under mud swept from Mount Umyeon on Wednesday, killing at least 15, following the heaviest downpours to hammer the South Korean capital in a century.
But Kim said the military had already cleared the area affected by the landslide.
"Chances are low that mines will be spotted," he said. "But we're preparing for any situation that may arise from the area. We have not yet received any report that the mines have been spotted."
The mines were placed after the 1950-53 Korean War, and a military official explained that most were removed between 1999 and 2006.
"We have placed warning signs across the mountain to warn residents and hikers," the official said.
An army official said all explosives that had been swept out of a unit in Yangju, Gyeonggi Province, Wednesday night were recovered by Thursday afternoon. Around 9 p.m. Wednesday, an Army ammunition depot in the northern town collapsed under a landslide, and explosives, such as mines and grenades, were lost. The official said, however, that they didn't present much danger since the landmines were separated from their fuses and the grenades were kept in wooden boxes.
The Joint Chiefs of Staff (JCS) has ordered subordinate units to check for any misplaced mines in regions damaged by landslides and heavy rains. The areas include Mount Umyeon as well as towns in Gyeonggi and Gangwon Provinces populated by front-line military units.
A JCS official urged people to report to police or nearby military units if they spot mines or objects believed to be explosives.