SEOUL, South Korea (AFP) — North Korea has recently laid tens of thousands of new landmines along its border, forcing its soldiers to work in grim conditions as they suffer multiple casualties, Seoul said Wednesday.

“Despite sweltering heat and the monsoon season, the North Korean military has laid down mines and erected wall fences along the front-line areas,” the defense ministry said in a statement.

“The newly planted mines are estimated to number in the tens of thousands,” it added.

During the months-long effort to strengthen defenses along the demilitarized zone — already one of the most heavily mined areas in the world — there have been at least 10 instances where mines exploded, resulting in “multiple casualties” among the soldiers, the ministry said.

North Korean soldiers mobilized for this effort have been living under “inadequate barracks conditions without weekends or change of duty, working 12 to 13 hours a day on average,” the ministry noted.