The military will expand operations to detect and remove landmines in the border regions next week after a dozen mines were collected from flood-damaged areas amid concern that some could have also been washed away from North Korea, officials said Friday.

Front-line military units have been working to search for mines that could have made their way south from the Demilitarized Zone (DMZ) and other border regions as heavy downpours have drenched the country for weeks. As of Friday, 12 mines have been collected.

Starting Monday, the military will expand the operation area to overall border regions, including those hit by landslides or flooding, with additional forces and equipment, the JCS said.

The US Forces Korea will also join the efforts with its mine detection and explosive ordnance disposal teams, officials said.

"The US military plans to send troops to Cheorwon and carry out operations after forming task forces with the South Korean military," an official said.

Millions of mines are believed to have been laid on the Korean Peninsula during the 1950-53 Korean War, and many are still buried in the DMZ, a 4-kilometer-wide buffer zone between the two Koreas, nearly 70 years after the war ended.

The defense ministry earlier heightened the level of emergency duty by one notch to the third and highest one to be fully prepared for the heavy rains.

Meanwhile, the defense ministry said it will exempt reservists residing in regions designated as special disaster zones due to recent heavy rains from the annual training slated for next month.

On Thursday, President Moon Jae-in designated 11 southern regions in the Jeolla and South Gyeongsang provinces as special disaster zones in addition to seven central and eastern areas designated last week.

"The defense ministry will continue to take active measures to support reservists in the special disaster zones and their families for an early recovery," it said in a release.

The recent downpours that pounded the central and southern regions have left 42 people dead or missing and more than 7,800 people displaced as of Wednesday. (Yonhap)