According to the paper, Pyongyang could have already managed to develop technology needed to construct smaller nuclear warheads to arm is missiles.
North Korean missile tests could be aimed at increasing the range of missiles, their precision and handling, the ministry added.
The white paper was written before Pyongyang carried out it two latest missile launches on July 4 and July 28, respectively. According to the state-run Korean Central News Agency (KCNA), the second test was successful.
On Saturday, the UN Security Council unanimously adopted a resolution tightening sanctions against North Korea, in particular banning UN member states from importing coal, iron ore, lead and seafood from the Asian country.