The ministry, in a white paper released Thursday, also called North Korea and its military an "enemy" to South Korea, Yonhap News Agency reported.
"Threats from North Korea's asymmetric warfare capabilities such as special forces, artillery pieces and weapons of mass destruction have been on a steady rise since 2008," Deputy Defense Minister Chang Kwang-il said.
Military officials in Seoul said Pyongyang has been focusing on unconventional or "asymmetric" weapons, such as improvised explosive devices or low-cost missiles, the South Korean news agency said. The white paper also confirmed North Korea deployed its new battle tank, believed to be based on the Soviet Union's T-72 tanks.
The report said the number of North Korean special forces increased to 200,000 from 180,000, Yonhap reported. Overall, the number of North Korean soldiers remained at about 1.19 million, but the military was reorganized to add four new divisions.
North Korea also is "presumed to have secured about 40 kilograms" of weapons-grade plutonium by reprocessing spent nuclear fuel rods, the paper said. Concern about Pyongyang's nuclear weapons program grew in November when officials revealed a uranium enrichment facility to a visiting U.S. scientist.
"Given that North Korea claimed that some 2,000 centrifuges are operational in November 2010, the North is presumed to have pushed for the highly enriched uranium program," the paper said.