South Korea is afraid of the North starting a "tunnel warfare". On both front and back side four [tunnels] have been discovered.
香港《亚洲周刊》4月21日（提前出版）一期报道 题：朝鲜半岛神经战 韩国严防地下坑道突袭
Hong Kong's "Asia Weekly" magazine in a beforehand edition on April 21 reported on the following subjects: War of nerves on the Korean peninsula. South Korea taking strict precautions against a surprise attack from underground tunnels.
North Korea's decisive battle may be triggered at any moment. A South Korean diplomat residing in China told "Asia Weekly" magazine: " Actually, North Korea is launching an offensive from air and earth. We have means to deal with that. Most to worry is the underground [attack]. As to the underground tunnels that we call 'Southern invasion tunnels', we have discovered four of them on, both, front and back side. But, after all, how many [exist] ? During many decades nobody could be precise about that. Their troops possibly already under our feet, [uneasiness about Northern brand appearing at any mile], easily at one stroke, mysteriously, this is utmost terrifying. "
[Source: mil.sohu 搜狐军事 quoting New China Network 新华网 on April 22, 2013]
America dispatches aircraft carrier Nimitz to proceed to the West Pacific for keeping watch on North Korea.
[Source: People's Network 人民网 quoting Global Network 环球网 on April 22, 2013. The report is mentioning a Japanese source of information.]
A visitor to "blueprint news" coming from San Diego, the home of USS Nimitz: