North Korean leader Kim Jong Un has inspected a facility that produces nuclear material and called for bolstering the country’s nuclear capability, state media reported Wednesday, as it ramps up pressure on the United States following the inauguration of President Donald Trump.

North Korean leader Kim Jong Un has called for bolstering nuclear forces this year during a visit to a nuclear material production base and nuclear weapons institute, state media KCNA reported on Wednesday.

South Korea 's Yonhap News Agency said North Korea might be using a vertical cold-launch system to fire the missiles. The system, which is commonly associated with submarine- and ship-based weapons, ejects a missile from its container before the missile ignites midair.