North Korea's Kim calls for scaling up weapons grade nuclear materials

North Korean leader Kim Jong Un called for scaling up the production of weapons-grade nuclear materials to increase the country's nuclear arsenal, saying it should be fully ready to use the weapons at any time, state media KCNA said on Tuesday.

Kim made the remarks during an inspection of the country's nuclear weapons programme where it tested trigger technology, KCNA said.

The military simulated a nuclear air explosion strike with two ground-to-ground tactical ballistic missiles during Monday's firing training, KCNA said in a separate dispatch.

A defence think tank also tested underwater strategic weapons systems, KCNA said.