No signs have been detected that North Korea dug underground tunnels into the South's capital areas, Seoul's defense ministry said Monday, dismissing recent claims of the government's cover-up of such penetration attempts as "groundless."

Hahn Sung-chu, a former two-star general in South Korea, has argued that North Korea carved out at least 84 underground tunnels that lead to the presidential office in central Seoul and a dozen others that connect with each other across the nation.

Hahn has long made such claims and raised aggressive campaigns in recent weeks by appearing on television programs at home and abroad. Videos carrying his argument during seminars have also been circulating online, stoking public security anxiety.

"Not a single sign was detected with regard to the claims about long underground tunnels by North Korea into Seoul and the surrounding capital areas," the defense ministry said in a statement after lawmakers raised such concerns during the regular parliamentary audit into the government.

Building one 60-kilometer tunnel that stretches from the border region to Seoul is supposed to leave 700,000 tons of rocks, but no such waste has been found by the military's reconnaissance assets, it noted.

As for the claims that the communist country employed tunnel boring machines for infiltration, the ministry said the former general appears to simply have mistaken Pyongyang's decades-old mining devices for big-ticket items.

"Chances are slim for North Korea to have 300 TBMs (as Hahan says), which cost 8 billion won ($7.6 million) per unit," the ministry said, adding that no drainage and ventilation facilities required for tunnel construction have been found so far.

"Such false claims cause public anxiety and hinder the military's normal operations. We will react sternly in accordance with the law," it noted.

Stressing that the government does see possibilities of the existence of such infiltration tunnels by the communist country, the military has launched operations to find them in 27 suspicious spots near the demilitarized zone, according to the ministry.

"Since 1982, our military has spent 2 billion won for drilling and exploring 21 areas near the border towns but has not spotted even one," the ministry said.

Between 1974 and 1990, South Korea discovered four secret tunnels from North Korea believed to be aimed at launching a surprise attack on Seoul. But none have been found since 1990. (Yonhap)