DPRK is the acronym for the North's official name, the Democratic People's Republic of Korea. The country often makes threats against the United States and South Korea.
Innovations have been made to improve nuclear weapons "in quality and quantity as required by the prevailing situation," the director was quoted as saying.
Late on Monday, the North's space agency said it was readying a new satellite for launch, indicating it may fire an upgraded long-range ballistic missile timed to a national anniversary next month.
North Korea declared in April 2013 at the height of tensions arising from Pyongyang's anger over joint military drills by U.S. and South Korean forces that it will restart all nuclear facilities.
The Yongbyon plant had been shut in 2007 under an agreement with five countries including the United States and China in exchange for diplomatic and economic incentives.