“They have set up screens on the roads and are working behind these screens, preparing to blow up the roads,” Li told reporters.
The operation could take place already on Monday, the representative of the committee admitted.
Tensions on the Korean Peninsula have increased for several weeks.
North Korea has accused South Korea of using drones three times to drop propaganda leaflets over North Korean territory and has threatened to respond with force if it happens again.
North Korea’s defense ministry said in a statement on Sunday that it had deployed several army units to the border and was “fully preparing to open fire” and that South Korea would “turn into piles of ashes” if attacked.
South Korea’s Unification Ministry spokesman Gu Byeong-sam said the move was likely motivated by a desire to strengthen North Korean unity by focusing on a common enemy.
Pyongyang often uses belligerent rhetoric in preparation for missile tests, which it has been banned from conducting by the United Nations.
Experts say a full-scale attack is unlikely given the superior firepower and numerical superiority of South Korea and its ally the United States.
However, the destruction of cross-border roads would be a major blow to decades of work towards a peaceful reunification of the two countries.
Last January, North Korean dictator Kim Jong-un amended the constitution to remove language on reunification and declared the South his “unchanging arch-enemy”.