The main threat is the deployment of 240-millimeter rocket launchers that reportedly have an increased range of about 70 kilometers, which makes them a threat to Seoul's southern outskirts.
The United States estimates North Korea has about 5,100 rocket launchers in its arsenal. Their positions along the border include 107mm, 122mm and 240mm weapons. Sources believe the 107mm weapons are being replaced by the new 240mm series.
"We are detecting signs that the north is deploying the improved 240-mm-caliber multiple rocket launchers, and the signs are they are showing up at some western and eastern front-line military units," the Yonhap source said.
Pyongyang has had the ability to hit Seoul with rockets and artillery for several years since the South Korean capital is located a short distance from the border.