London: South Korean military chiefs fear North Korean leader Kim Jong-Un`s troops - as many as 30,000 - have dug a series of tunnels reaching behind the South`s defensive lines.
As the South braced itself for war between the countries for the first time since 1953, a military source said they are at high alert and have seen little movement. He, however, said that the North has already tried four times since the armistice to launch a tunnel invasion, reports the Mirror.
The source said that four have been found over the years - three in the 70s and the last in 1990. He said they haven`t found one since then, but are sure they are there.
More than four million died in the 1950-53 war, sparked by a Soviet-backed North invasion that ultimately failed. Since then North Korea`s brutal and paranoid regime has flooded the south with spies, trying to track down 24,614 refugees who have fled across the border since the armistice.
The Korean crisis has been triggered by Kim`s increasingly aggressive threats of nuclear strikes against America and its South Korean allies.
Sanctions against the state were tightened after Pyongyang`s third nuclear test in February and Kim`s belligerence has prompted US warships to head towards the Korean peninsular.
Kim Jong-Un has authorised a nuclear strike on America, moved missiles capable of 2,500-mile strikes to North Korea`s eastern shore and the US has bolstered its defences of the Pacific island of Guam.
South Korea has deployed two destroyers off the east coast ready to shoot down any missiles.