North Korea appears to have rebuilt some of its destroyed guard posts inside the Demilitarized Zone separating the two Koreas with concrete structures, a military source said Friday.

Last November, the North began rebuilding the guard posts with wooden material after scrapping a 2018 inter-Korean military agreement designed to reduce tensions along the border, according to Seoul's defense officials.

"We have detected that North Korea has built concrete guard posts at the destroyed guard post (sites)," the source said, without providing further details.

As part of the 2018 deal signed under the previous liberal President Moon Jae-in, the two Koreas demolished 10 guard posts inside the DMZ each and disarmed an additional one each, leaving the North with some 150 guard posts and South Korea with 67 of them.

The North, however, vowed to restore all military measures halted under the agreement after Seoul partially suspended the deal in protest of the North's successful launch of its first military spy satellite on Nov. 21.

The construction of concrete structures suggests the North could operate the guard posts in full-scale, compared with temporary wooden structures.

The South Korean military has also detected North Korean troops installing mines on a road connecting South Korea to the now-shuttered joint industrial complex in the North's border city of Kaesong.

Military authorities believe the move is intended to completely shut down the road so that it will no longer be used.

The South shut down the inter-Korean complex in 2016 in response to North Korea's nuclear and missile tests.

Tensions have recently heightened after North Korean leader Kim Jong-un defined inter-Korean ties as relations "between two states hostile to each other" and ordered preparations "to suppress the whole territory" of South Korea in a contingency at a year-end ruling party meeting. (Yonhap)