Nam Jong Chol, a senior researcher at North Korea's foreign ministry-affiliated Institute for Disarmament and Peace, said the North has strengthened its nuclear capability, Yonhap News Agency said.
"The U.S.'s hostile policy against [North Korea] has compelled us to possess self-defensive nuclear weapons," he said during a forum organized by the Council for Security Cooperation in the Asia Pacific.
"The U.S.'s stance is a main reason for [North Korea] to take measures to strengthen its nuclear deterrence in quality and in quantity," he added.
Nam also warned should there be "any military conflict on the Korean Peninsula, it will surely ignite a war."
Six-party talks about North Korea's nuclear program involving the two Koreas, the United States, China, Russia and Japan stalled in 2008. Pyongyang has repeatedly shown interest in returning to the talks, but the South and the United States have demanded the North first display good-faith steps toward denuclearization.