The unidentified expert told South Korea's Yonhap News Agency that North Korea's missile program has progressed from tactical artillery rockets to short-range and medium-range ballistic missiles.
North Korea also has been trying to make a nuclear warhead with a greater range but not much is known about it, he said.
"North Korea has produced about 100 missiles annually since the 1990s and its capacity is believed to have made progress. Among the missiles manufactured so far, up to 70 percent could attack South Korea," the expert told Yonhap.
The North's latest long-range Taepodong missiles evolved from its own versions of the Scud as well as medium-range Nodong missile, he said.
North Korea is estimated to have about 700 Scuds with a range of up to 310 miles, 300 Nodong missiles with a range of up to 807 miles and a small number of long-range missiles, such as Musudan, that can reach Japan and U.S. military bases in the Pacific, the expert said.
"Iran's Shahab missiles, which were developed based on the North's Nodong missile, also applied the triconic design to reduce the warhead's payload from (2,200 pounds to 1,540 pounds)," he said. "This leads to speculation that the two countries may have closely cooperated on missile technology."
The North launched a three-stage rocket in December and conducted its third nuclear test in February. However, the expert told Yonhap he doubts Pyongyang has mastered technology to develop a nuclear warhead that can be fitted on a long-range missile that can strike the U.S. mainland.